Sophisms and paradoxes. Sophisms and logical paradoxes Paradoxes in logic

LOGICAL PARADOX

LOGICAL PARADOX

a proposition that is not yet obvious at first, but, contrary to expectations, expresses the truth. In ancient logic, a paradox was called a paradox, the ambiguity of which relates primarily to its correctness or incorrectness. In modern mathematics, paradoxes are actually mathematical ones. aporia.

Philosophical Encyclopedic Dictionary. 2010 .

LOGICAL PARADOX

The development of modern logical methods has led to new logical paradoxes. For example, Brouwer pointed out the following paradox of classical existence: in any sufficiently strong classical theory there is a provable formula of the form ExA(x), for which it is impossible to construct any specific t such that A(t) is provable.

In particular, it is impossible to construct a single non-standard model of real numbers in set theory, although such models can be proven. This paradox shows that the concepts of existence and constructability are irreversibly divergent in classical mathematics.

Further, non-standard models, which required an explicit distinction between language and metalanguage, led to the following paradox: “The set of all standard real numbers is part of a non-standard finite set. Thus, it can be part of the finite.”

This paradox sharply contradicts the ordinary understanding of the relationship between the finite and the infinite. It is based on the fact that “being standard” belongs to a metalanguage, but can be accurately interpreted in a non-standard model. Therefore, in the non-standard model, one can talk about the truth and falsity of any mathematical statements that include the concept of “being (non-standard", but for them the properties of the standard model are not required to be preserved, with the exception of logical tautologies. This paradox became the basis of the theory of semisets, in which there can be subclasses of sets .

And finally, the last class of logical paradoxes arises at the boundaries between formalized and informal concepts. Let's consider one of them (Simon); “Anything that can be expressed precisely can be expressed in the language of Turing machines. Therefore, in the humanities only those models that can be expressed in the language of Turing machines can be considered. Moreover, according to the method of diagonalization, any precise objection to a given point of view is itself translated to and included in Turing machines.”

This paradox stimulated the emergence of the theory of non-formalizable concepts, but due to the fact that it was not immediately recognized as a paradox, at the same time it led to sad consequences, since this one, in which fundamental expressibility (requiring unrealistic resources) and real descriptions were confused, was perceived as accurate reasoning and , as noted in works on cognitive science, paralyzed Western psychology for almost 10 years. The rejection of Simon's argument after realizing its sophistic nature was structured in such a way that it led to a complete rejection of precise concepts and thereby essentially served as the motivation for movements such as postmodernism. In this case, a logical mistake was made in replacing a contradictory judgment with the opposite one.

Ya. Ya. Nepeyvoda

New Philosophical Encyclopedia: In 4 vols. M.: Thought. Edited by V. S. Stepin. 2001 .

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It is necessary to distinguish from sophistry logical paradoxes(from Greek paradoxes –"unexpected, strange") A paradox in the broad sense of the word is something unusual and surprising, something that diverges from usual expectations, common sense and life experience. A logical paradox is such an unusual and surprising situation when two contradictory propositions are not only simultaneously true (which is impossible due to the logical laws of contradiction and the excluded middle), but also follow from each other and condition each other. If sophistry is always some kind of trick, a deliberate logical error that can be detected, exposed and eliminated, then a paradox is an insoluble situation, a kind of mental impasse, a “stumbling block” in logic: throughout its history, many different methods have been proposed overcoming and eliminating paradoxes, however, none of them is still exhaustive, final and generally accepted.

The most famous logical paradox is the “liar” paradox. He is often called the “king of logical paradoxes.” It was opened back in Ancient Greece. According to legend, the philosopher Diodorus Kronos vowed not to eat until he resolved this paradox and died of hunger, having achieved nothing; and another thinker, Philetus of Kos, fell into despair from the inability to find a solution to the “liar” paradox and committed suicide by throwing himself from a cliff into the sea. There are several different formulations of this paradox. It is formulated most briefly and simply in a situation where a person utters a simple phrase: I am a liar. Analysis of this elementary and ingenuous at first glance statement leads to a stunning result. As you know, any statement (including the above) can be true or false. Let us consider successively both cases, in the first of which this statement is true, and in the second it is false.

Let's assume that the phrase I am a liar true, i.e. the person who uttered it told the truth, but in this case he is really a liar, therefore, by uttering this phrase, he lied. Now suppose that the phrase I am a liar is false, that is, the person who uttered it lied, but in this case he is not a liar, but a truth-teller, therefore, by uttering this phrase, he told the truth. It turns out something amazing and even impossible: if a person told the truth, then he lied; and if he lied, then he told the truth (two contradictory propositions are not only simultaneously true, but also follow from each other).

Another famous logical paradox discovered at the beginning of the 20th century by the English logician and philosopher

Bertrand Russell, is the paradox of the “village barber”. Let's imagine that in a certain village there is only one barber who shaves those residents who do not shave themselves. Analysis of this simple situation leads to an extraordinary conclusion. Let's ask ourselves: can a village barber shave himself? Let's consider both options, in the first of which he shaves himself, and in the second he does not.

Let us assume that the village barber shaves himself, but then he is one of those village residents who shave themselves and whom the barber does not shave, therefore, in this case, he does not shave himself. Now suppose that the village barber does not shave himself, but then he belongs to those villagers who do not shave themselves and whom the barber shaves, therefore, in this case, he shaves himself. As we see, the incredible thing turns out: if a village barber shaves himself, then he does not shave himself; and if he does not shave himself, then he shaves himself (two contradictory propositions are simultaneously true and mutually condition each other).

The “liar” and “village barber” paradoxes, along with other similar paradoxes, are also called antinomies(from Greek antinomia“contradiction in the law”), i.e., reasoning in which it is proven that two statements that deny each other follow from one another. Antinomies are considered to be the most extreme form of paradoxes. However, quite often the terms “logical paradox” and “antinomy” are considered synonymous.

A less surprising formulation, but no less famous than the paradoxes of the “liar” and the “village barber,” is the paradox of “Protagoras and Euathlus,” which, like the “liar,” appeared in Ancient Greece. It is based on a seemingly simple story, which is that the sophist Protagoras had a student Euathlus, who took lessons in logic and rhetoric from him

(in this case – political and judicial eloquence). Teacher and student agreed that Euathlus would pay Protagoras his tuition fees only if he won his first trial. However, upon completion of the training, Evatl did not participate in any process and, of course, did not pay the teacher any money. Protagoras threatened him that he would sue him and then Euathlus would have to pay in any case. “You will either be sentenced to pay a fee, or you will not be sentenced,” Protagoras told him, “if you are sentenced to pay, you will have to pay according to the verdict of the court; if you are not sentenced to pay, then you, as the winner of your first trial, will have to pay according to our agreement.” To this Evatl answered him: “Everything is correct: I will either be sentenced to pay a fee, or I will not be sentenced; if I am sentenced to pay, then I, as the loser of my first lawsuit, will not pay according to our agreement; if I am not sentenced to pay, then I will not pay the court’s verdict.” Thus, the question of whether Euathlus should pay Protagoras a fee or not is indecisive. The agreement between teacher and student, despite its completely innocent appearance, is internally, or logically, contradictory, since it requires performing an impossible action: Evatl must both pay for the training and not pay at the same time. Because of this, the agreement itself between Protagoras and Euathlus, as well as the question of their litigation, represents nothing more than a logical paradox.

Separate group paradoxes are aporia(from Greek aporia“difficulty, bewilderment”) - reasoning that shows the contradictions between what we perceive with our senses (see, hear, touch, etc.) and what can be mentally analyzed (in other words, the contradictions between the visible and the imaginable) . The most famous aporia was put forward by the ancient Greek philosopher Zeno of Elea, who argued that the movement we observe everywhere cannot be made the subject of mental analysis, that is, movement can be seen, but cannot be thought. One of his aporias is called “Dichotomy” (Greek. dihotomia"bisection"). Suppose a certain body needs to go from point A to point IN. There is no doubt that we can see how a body, leaving one point, after some time reaches another. However, let's not trust our eyes, which tell us that the body is moving, and let's try to perceive the movement not with our eyes, but with our thoughts; let's try not to see it, but to think about it. In this case, we will get the following. Before you go all the way from the point A to point IN, the body needs to go half of this way, because if it doesn’t go half the way, then, of course, it won’t go the whole way. But before the body goes halfway, it needs to go 1/4 of the way. However, before it goes this 1/4 part of the way, it needs to go 1/8 part of the way; and even before that he needs to go 1/16th of the way, and before that - 1/32nd, and before that - 1/64th, and before that - 1/128th, and so on ad infinitum. So, to go from point A to point IN, the body must travel an infinite number of segments of this path. Is it possible to go through infinity? Impossible! Therefore, the body will never be able to complete its journey. Thus, the eyes testify that the path will be passed, but thought, on the contrary, denies this (the visible contradicts the conceivable).

Another famous aporia of Zeno of Elea - “Achilles and the Tortoise” - says that we may well see how the fleet-footed Achilles catches up and overtakes the tortoise slowly crawling in front of him; However, mental analysis leads us to the unusual conclusion that Achilles can never catch up with the tortoise, although he moves 10 times faster than it. When he covers the distance to the turtle, then during the same time (after all, it also moves) it will travel 10 times less (since it moves 10 times slower), namely 1/10 of the path that Achilles traveled, and this 1/10th will be in front of it.

When Achilles travels this 1/10th of the way, the turtle will cover 10 times less distance in the same time, i.e. 1/100th of the way and will be ahead of Achilles by this 1/100th. When he passes 1/100th of the path separating him and the turtle, then in the same time it will cover 1/1000th of the path, still remaining ahead of Achilles, and so on ad infinitum. So, we are again convinced that the eyes tell us about one thing, and the thought - about something completely different (the visible is denied by the thinkable).

Another aporia of Zeno - “Arrow” - invites us to mentally consider the flight of an arrow from one point in space to another. Our eyes, of course, indicate that the arrow is flying or moving. However, what will happen if we try, abstracting from the visual impression, to imagine its flight? To do this, let’s ask ourselves a simple question: where is the flying arrow now? If, in answer to this question, we say, for example, She's here now or She's here now or She's there now then all these answers will mean not the flight of the arrow, but precisely its immobility, because being Here, or here, or there - means to be at rest and not to move. How can we answer the question - where is the flying arrow now - in such a way that the answer reflects its flight, and not its immobility? The only possible answer in this case should be this: She is everywhere and nowhere now. But is it possible to be everywhere and nowhere at the same time? So, when trying to imagine the flight of an arrow, we came across a logical contradiction, an absurdity - the arrow is everywhere and nowhere. It turns out that the movement of the arrow can be seen, but it cannot be conceived, as a result of which it is impossible, like any movement in general. In other words, moving, from the point of view of thought, and not from sensory perceptions, means being in a certain place and not being in it at the same time, which, of course, is impossible.

In his aporia, Zeno brought together in a “confrontation” the data of the senses (talking about the multiplicity, divisibility and movement of everything that exists, assuring us that the fleet-footed Achilles will catch up with the slow tortoise, and the arrow will reach the target) and speculation (which cannot conceive of movement or multiplicity objects of the world, without falling into contradiction).

Once, when Zeno was demonstrating to a crowd of people the inconceivability and impossibility of movement, among his listeners was the equally famous philosopher Diogenes of Sinope in Ancient Greece. Without saying anything, he stood up and began to walk around, believing that by doing this he was proving better than any words the reality of movement. However, Zeno was not at a loss and answered: “Don’t walk and don’t wave your hands, but try to solve this complex problem with your mind.” Regarding this situation, there is even the following poem by A. S. Pushkin:

There is no movement, said the bearded sage,

The other fell silent and began to walk in front of him.

He could not have objected more strongly;

Everyone praised the intricate answer.

But, gentlemen, this is a funny case

Another example comes to mind:

After all, every day the Sun walks before us,

However, stubborn Galileo is right.

And indeed, we see quite clearly that the Sun moves across the sky every day from east to west, but in fact it is motionless (in relation to the Earth). So why don't we assume that other objects that we see moving may actually be motionless, and not rush to say that the Eleatic thinker was wrong?

As already noted, many ways to resolve and overcome paradoxes have been created in logic. However, none of them is without objections and is not generally accepted. Consideration of these methods is a long and tedious theoretical procedure, which remains beyond our attention in this case. An inquisitive reader will be able to get acquainted with various approaches to solving the problem of logical paradoxes in additional literature. Logical paradoxes provide evidence that logic, like any other science, is not complete, but constantly evolving. Apparently, paradoxes point to some deep problems of logical theory, lift the veil over something not yet entirely known and understood, and outline new horizons in the development of logic.

It is known that formulating a problem is often more important and more difficult than solving it. “In science,” wrote the English chemist F. Soddy, “a problem, properly posed, is more than half solved. The mental preparation process required to figure out that a certain problem exists often takes more time than solving the problem itself.”
The forms in which a problem situation manifests itself and is recognized are very diverse. It does not always reveal itself in the form of a direct question that arises at the very beginning of the study. The world of problems is as complex as the process of cognition that generates them. Identifying problems is related to the very essence of creative thinking. Paradoxes are the most interesting case of implicit, unquestioning ways of posing problems. Paradoxes are common in the early stages of the development of scientific theories, when the first steps are taken in an as yet unexplored area and the most general principles approach to it.

Paradoxes and logic

In a broad sense, a paradox is a position that sharply diverges from generally accepted, established, orthodox opinions. “Generally accepted opinions and what is considered a long-decided matter are most often worthy of investigation” (GLichtenberg). The paradox is the beginning of such research.
A paradox in a narrower and more specialized sense is two opposing, incompatible statements, for each of which there are seemingly convincing arguments.
The most extreme form of paradox is antinomy, a reasoning that proves the equivalence of two statements, one of which is a negation of the other.
Paradoxes are especially famous in the most rigorous and exact sciences—mathematics and logic. And this is no coincidence.

Logics- abstract science. There are no experiments in it, there are not even facts in the usual sense of the word. When constructing its systems, logic ultimately proceeds from the analysis of real thinking. But the results of this analysis are synthetic and undifferentiated. They are not statements of any individual processes or events that the theory should explain. Such an analysis obviously cannot be called observation: a specific phenomenon is always observed.
Designing new theory, a scientist usually starts from facts, from what can be observed in experience. No matter how free his creative imagination may be, it must take into account one indispensable circumstance: a theory makes sense only if it is consistent with the facts relating to it. A theory that diverges from facts and observations is far-fetched and has no value.
But if in logic there are no experiments, no facts and no observation itself, then what is holding back logical fantasy? What factors, if not facts, are taken into account when creating new logical theories?
The discrepancy between logical theory and the practice of actual thinking is often revealed in the form of a more or less acute logical paradox, and sometimes even in the form of a logical antinomy, which speaks of the internal inconsistency of the theory. This precisely explains the importance attached to paradoxes in logic, and the great attention they enjoy in it.

Variants of the Liar Paradox

The most famous and, perhaps, the most interesting of all logical paradoxes is the “Liar” paradox. It was he who mainly glorified the name of Eubulides of Miletus, who discovered it.
There are variations of this paradox or antinomy, many of which are only apparently paradoxical.
In the simplest version of “Liar,” a person utters just one phrase: “I’m lying.” Or he says: “The statement I am now making is false.” Or: “This statement is false.”

If the statement is false, then the speaker told the truth, and that means what he said is not a lie. If the statement is not false, but the speaker claims that it is false, then his statement is false. It turns out, therefore, that if the speaker is lying, he is telling the truth, and vice versa.

In the Middle Ages, the following formulation was common:

“What Plato said is false,” says Socrates.

“What Socrates said is the truth,” says Plato.

The question arises, which of them expresses the truth and which is a lie?
Here is a modern rephrasing of this paradox. Let's say that on the front side of the card there are only the words written: “On the other side of this card there is a true statement written.” Clearly these words represent a meaningful statement. Turning the card over, we must either find the promised statement, or there is none. If it is written on the back, then it is either true or not. However, on the back are the words: “There is a false statement written on the other side of this card” - and nothing more. Let's assume that the statement on the front is true. Then the statement on the back must be true and therefore the statement on the front must be false. But if the statement on the front side is false, then the statement on the back side must also be false, and therefore the statement on the front side must be true. The result is a paradox.
The Liar paradox made a huge impression on the Greeks. And it's easy to see why. The question it poses seems quite simple at first glance: does he lie who only says that he lies? But the answer “yes” leads to the answer “no”, and vice versa. And reflection does not clarify the situation at all. Behind the simplicity and even routineness of the question, it reveals some obscure and immeasurable depth.
There is even a legend that a certain Filit Kossky, despairing of resolving this paradox, committed suicide. They also say that one of the famous ancient Greek logicians, Diodorus Kronos, already in his declining years made a vow not to eat until he found the solution to the “Liar”, and soon died without achieving anything.
In the Middle Ages, this paradox was classified as one of the so-called undecidable sentences and became the object of systematic analysis. In modern times, “The Liar” did not attract any attention for a long time. They did not see any, even minor, difficulties in him regarding the use of language. And only in our so-called modern times The development of logic has finally reached a level where the problems that seem to stand behind this paradox have become possible to formulate in strict terms.
Now “The Liar” - this typical former sophism - is often called the king of logical paradoxes. An extensive scientific literature is devoted to it. And yet, as with many other paradoxes, it remains not entirely clear what problems are hidden behind it and how to get rid of it.

Language and metalanguage

Now “The Liar” is usually considered a characteristic example of the difficulties that arise from the confusion of two languages: the language that speaks about a reality that lies outside itself, and the language that speaks about the first language itself.

In everyday language there is no distinction between these levels: we speak about both reality and language in the same language. For example, a person whose native language is Russian does not see any particular difference between the statements: “Glass is transparent” and “It is true that glass is transparent,” although one of them is about glass, and the other is about a statement about glass.
If someone had the idea of ​​​​the need to talk about the world in one language, and about the properties of this language in another, he could use two different existing languages, say Russian and English. Instead of simply saying: “Cow is a noun,” one would say “Cow is a noun,” and instead of: “The assertion “Glass is not transparent” is false.” With two different languages ​​used in this way, what is said about the world would clearly differ from what is said about the language with which the world is spoken. In fact, the first statements would relate to the Russian language, while the second would refer to English.

If our language expert further wanted to speak out about some circumstances related to the English language, he could use another language. Let's say German. To talk about this last point, one could resort, let’s say, to Spanish etc.
Thus, what emerges is a kind of ladder, or hierarchy, of languages, each of which is used for a very specific purpose: in the first they speak about the objective world, in the second about this first language, in the third about the second language, etc. Such a distinction between languages ​​according to their area of ​​application is a rare occurrence in everyday life. But in sciences that specifically deal with languages, like logic, it sometimes turns out to be very useful. The language used to talk about the world is usually called object language. The language used to describe the subject language is called a metalanguage.

It is clear that if language and metalanguage are distinguished in this way, the statement “I am lying” can no longer be formulated. It speaks of the falsity of what is said in Russian, and, therefore, belongs to the metalanguage and must be expressed in English language. Specifically, it should sound like this: “Everything I speak in Russian is false” (“Everything I said in Russian is false”); this English statement says nothing about himself, and no paradox arises.
The distinction between language and metalanguage makes it possible to eliminate the “Liar” paradox. Thus, it becomes possible to correctly, without contradiction, define the classical concept of truth: a statement is true if it corresponds to the reality it describes.
The concept of truth, like all other semantic concepts, is relative in nature: it can always be attributed to a specific language.

As the Polish logician ATarski showed, the classical definition of truth must be formulated in a language broader than the language for which it is intended. In other words, if we want to indicate what the phrase “a statement true in a given language” means, we must, in addition to expressions of this language, also use expressions that are not in it.
Tarski introduced the concept of a semantically closed language. Such a language includes, in addition to its expressions, their names, and also, what is important to emphasize, statements about the truth of the sentences formulated in it.

There is no boundary between language and metalanguage in a semantically closed language. Its means are so rich that they allow not only to assert something about extra-linguistic reality, but also to evaluate the truth of such statements. These means are sufficient, in particular, to reproduce the antinomy “Liar” in the language. A semantically closed language thus turns out to be internally contradictory. Every natural language is obviously semantically closed.
The only acceptable way to eliminate antinomy, and hence internal inconsistency, according to Tarski, is to abandon the use of a semantically closed language. This path is acceptable, of course, only in the case of artificial, formalized languages ​​that allow a clear division into language and metalanguage. In natural languages, with their obscure structure and the ability to talk about everything in the same language, this approach is not very realistic. It makes no sense to raise the question of the internal consistency of these languages. Their rich expressive possibilities also have their downside - paradoxes.

Other solutions to the paradox

So there are statements that speak of their own truth or falsity. The idea that these kinds of statements are not meaningful is a very old one. It was defended by the ancient Greek logician Chrysippus.
In the Middle Ages, the English philosopher and logician W. Ockham stated that the statement “Every statement is false” is meaningless, since it speaks, among other things, about its own falsity. A contradiction directly follows from this statement. If every statement is false, then this applies to the given statement itself; but the fact that it is false means that not every statement is false.

The situation is similar with the statement “Every statement is true.” It should also be classified as meaningless and also leads to a contradiction: if every statement is true, then the negation of this statement itself is true, that is, the statement that not every statement is true.
Why, however, cannot a statement meaningfully speak of its own truth or falsity?
Already a contemporary of Occam, the French philosopher of the 14th century. J. Buridan did not agree with his decision. From the point of view of ordinary ideas about meaninglessness, expressions like “I am lying”, “Every statement is true (false)”, etc. quite meaningful. What you can think about, you can speak out about - this is the general principle of Buridan. A person can think about the truth of the statement that he utters, which means that he can speak about it. Not all self-talk is nonsensical. For example, the statement “This sentence is written in Russian” is true, but the statement “There are ten words in this sentence” is false. And both of them make perfect sense. If it is allowed that a statement can speak about itself, then why is it not capable of speaking meaningfully about such a property as truth?
Buridan himself considered the statement “I am lying” not meaningless, but false. He justified it like this.

When a person asserts a proposition, he thereby asserts that it is true. If a sentence says about itself that it is itself false, then it is only a shortened formulation of a more complex expression that asserts both its truth and its falsity. This expression is contradictory and therefore false. But it is by no means meaningless.

Buridan's argument is still sometimes considered convincing.
There are other areas of criticism of the solution to the “Liar” paradox, which was developed in detail by Tarski. Is there really no antidote to paradoxes of this type in semantically closed languages ​​- and all natural languages ​​are such?
If this were so, then the concept of truth could be strictly defined only in formalized languages. Only in them is it possible to distinguish between the subject language in which one talks about the world around us, and the metalanguage in which one speaks about this language. This hierarchy of languages ​​is built on the model of acquisition foreign language with the help of a native. The study of such a hierarchy has led to many interesting conclusions, and in certain cases it is significant. But it is not in natural language. Will this discredit him? And if so, to what extent? After all, the concept of truth is still used in it, and usually without any complications. Is the introduction of hierarchy the only way excluding paradoxes like “Liar?”

In the 1930s, the answers to these questions seemed undoubtedly affirmative. However, now the former unanimity is no longer there, although the tradition of eliminating paradoxes of this type by “stratifying” the language remains dominant.
IN Lately Egocentric expressions are gaining more and more attention. They contain words like “I”, “this”, “here”, “now”, and their truth depends on when, by whom, and where they are used.

In the statement “This statement is false,” the word “it” appears. Which object exactly does it refer to? “Liar” may be saying that the word “it” is not relevant to the meaning of the statement. But then what does it refer to, what does it mean? And why can't this meaning still be denoted by the word "this"?
Without going into details here, it is only worth noting that in the context of the analysis of egocentric expressions, “Liar” is filled with a completely different content than before. It turns out that he no longer warns against confusing language and metalanguage, but points out the dangers associated with the incorrect use of the word “it” and similar egocentric words.
The problems associated with “The Liar” over the centuries have changed radically depending on whether it was seen as an example of ambiguity, or as an expression that appears externally as an example of a confusion of language and metalanguage, or, finally, as a typical example of the misuse of egocentric expressions. And there is no certainty that other problems will not be associated with this paradox in the future.

The famous modern Finnish logician and philosopher G. von Wright wrote in his work dedicated to “The Liar” that this paradox should in no case be understood as a local, isolated obstacle that can be eliminated with one inventive movement of thought. “Liar” touches many of the most important topics logic and semantics. This is the definition of truth, and the interpretation of contradiction and evidence, and a whole series of important differences: between a sentence and the thought it expresses, between the use of an expression and its mention, between the meaning of a name and the object it denotes.
The situation is similar with other logical paradoxes. “The antinomies of logic,” writes von Wrigg, “have puzzled us since their discovery and will probably always puzzle us. We must, I think, regard them not so much as problems awaiting solution, but as inexhaustible raw material for thought. They are important because thinking about them touches on the most fundamental questions of all logic, and therefore of all thinking.”

To conclude this conversation about “The Liar,” we can recall a curious episode from the time when formal logic was still taught in school. In a logic textbook published in the late 40s, eighth grade schoolchildren were offered homework- as a warm-up, so to speak, to find the mistake made in this seemingly simple statement: “I’m lying.” And, although it may not seem strange, it was believed that the majority of schoolchildren successfully coped with this task.

§ 2. Russell's paradox

The most famous of the paradoxes discovered already in our century is the antinomy discovered by B. Russell and communicated by him in a letter to G. Ferge. The same antinomy was discussed simultaneously in Göttingen by the German mathematicians Z. Zermelo and D. Hilbert.
The idea was in the air, and its publication had the effect of a bomb exploding. This paradox caused, according to Hilbert, the effect of a complete catastrophe in mathematics. The most simple and important logical methods, the most common and useful concepts are under threat.
It immediately became obvious that neither in logic nor in mathematics, in the entire long history of their existence, absolutely nothing had been developed that could serve as a basis for. eliminating the antinomy. A departure from conventional ways of thinking was clearly necessary. But from what place and in what direction? How radical would it be to break away from established ways of theorizing?
With further research into the antinomy, the conviction of the need for a fundamentally new approach grew steadily. Half a century after its discovery, specialists in the foundations of logic and mathematics L. Frenkel and I. Bar-Hillel already stated without any reservations: “We believe that any attempts to get out of the situation using traditional (that is, those in use before the 20th century) ways of thinking , which have so far consistently failed, are obviously insufficient for this purpose.”
The modern American logician H. Curry wrote a little later about this paradox: “In terms of logic known in the 19th century, the situation simply could not be explained, although, of course, in our educated age there may be people who will see (or think that they will see ), what is the mistake.”

Russell's paradox in its original form is connected with the concept of a set, or a class.
We can talk about sets various objects, for example, about the set of all people or the set of natural numbers. An element of the first set will be any individual person, an element of the second - every natural number. It is also possible to consider the sets themselves as some objects and speak of sets of sets. One can even introduce such concepts as the set of all sets or the set of all concepts.

Set of ordinary sets

Regarding any arbitrary set, it seems reasonable to ask whether it is its own element or not. Sets that do not contain themselves as an element will be called ordinary. For example, the set of all people is not a person, just as the set of atoms is not an atom. Sets that are their own elements will be unusual. For example, a set that unites all sets is a set and therefore contains itself as an element.
Let us now consider the set of all ordinary sets. Since it is many, one can also ask about it, whether it is ordinary or unusual. The answer, however, turns out to be discouraging. If it is ordinary, then, according to its definition, it must contain itself as an element, since it contains all ordinary sets. But this means that it is an unusual set. The assumption that our set is an ordinary set thus leads to a contradiction. This means it cannot be ordinary. On the other hand, it cannot be unusual either: an unusual set contains itself as an element, and the elements of our set are only ordinary sets. As a result, we come to the conclusion that the set of all ordinary sets cannot be either an ordinary or an unusual set.

So, the set of all sets that are not proper elements is its own element if and only if it is not such an element. This is a clear contradiction. And it was obtained on the basis of the most plausible assumptions and with the help of seemingly indisputable steps. The contradiction suggests that such a set simply does not exist. But why can't it exist? After all, it consists of objects that satisfy a clearly defined condition, and the condition itself does not seem somehow exceptional or unclear. If such a simply and clearly defined set cannot exist, then what, exactly, is the difference between possible and impossible sets? The conclusion about the non-existence of the set in question sounds unexpected and causes concern. It makes our general concept of set amorphous and chaotic, and there is no guarantee that it cannot give rise to some new paradoxes.

Russell's paradox is remarkable for its extreme generality. To construct it, you do not need any complex technical concepts, as in the case of some other paradoxes; the concepts of “set” and “element of set” are sufficient. But this simplicity speaks precisely of its fundamental nature: it touches on the deepest foundations of our reasoning about sets, since it is not talking about some special cases, and about sets in general.

Other versions of the paradox

Russell's paradox is not specifically mathematical in nature. It uses the concept of a set, but does not touch on any special properties related specifically to mathematics.
This becomes obvious if we reformulate the paradox in purely logical terms.

For each property one can, in all likelihood, ask whether it applies to itself or not.
The property of being hot, for example, does not apply to itself, since it is not itself hot; the property of being concrete also does not refer to itself, for it is an abstract property. But the property of being abstract, being abstract, is applicable to oneself. Let us call these self-inapplicable properties inapplicable. Does the property of being inapplicable to oneself apply? It turns out that an inapplicability is inapplicable only if it is not. This is, of course, paradoxical.
The logical, property-related version of Russell's antinomy is just as paradoxical as the mathematical, set-related version of it.
Russell also proposed the following popular version of the paradox he discovered.

Let's imagine that the council of one village defined the duties of a barber as follows: to shave all the men in the village who do not shave themselves, and only these men. Should he shave himself? If so, then he will treat those who shave themselves, but those who shave themselves, he should not shave. If not, he will be one of those who do not shave themselves, and therefore he will have to shave himself. We thus come to the conclusion that this barber shaves himself if and only if he does not shave himself. This is, of course, impossible. The argument about a hairdresser rests on the assumption that such a hairdresser exists. The resulting contradiction means that this assumption is false, and there is no resident of the village who would shave all those and only those villagers who do not shave themselves.
The duties of a hairdresser do not seem contradictory at first glance, so the conclusion that it cannot exist sounds somewhat unexpected. But this conclusion is not paradoxical. The condition that the village barber must satisfy is in fact internally contradictory and, therefore, impossible to fulfill. There cannot be such a barber in the village for the same reason that there is no person in it who is older than himself or who was born before his birth.
The argument about the hairdresser can be called a pseudo-paradox. In its course, it is strictly similar to Russell’s paradox and this is why it is interesting. But it is still not a true paradox.

Another example of the same pseudo-paradox is the famous argument about the catalogue.
A certain library decided to compile a bibliographic catalogue, which would include all those and only those bibliographic catalogs that do not contain links to themselves. Should such a directory include a link to itself?
It is not difficult to show that the idea of ​​creating such a catalog is impracticable; it simply cannot exist, since it must simultaneously include a reference to itself and not include it.
It is interesting to note that cataloging all directories that do not contain a reference to themselves can be thought of as an endless, never-ending process. Let's assume that at some point a directory, say K1, was compiled, including all directories different from it that do not contain links to themselves. With the creation of K1, another directory appeared that did not contain a link to itself. Since the problem is to create a complete catalog of all catalogs that do not mention themselves, it is obvious that K1 is not a solution. He doesn't mention one of those directories—himself. By including this mention of himself in K1, we get catalog K2. It mentions K1, but not K2 itself. By adding such a mention to K2, we get KZ, which is again incomplete due to the fact that it does not mention itself. And on and on without end.

§ 3. Paradoxes of Grelling and Berry

An interesting logical paradox was discovered by German logicians K. Grelling and L. Nelson (Grelling's paradox). This paradox can be formulated very simply.

Autological and heterological words

Some property words have the very property they name. For example, the adjective “Russian” is itself Russian, “polysyllabic” is itself polysyllabic, and “five-syllable” itself has five syllables. Such words referring to themselves are called self-valued, or autological.
There are not many similar words; the vast majority of adjectives do not have the properties that they name. “New” is not, of course, new, “hot” is hot, “one-syllable” is one syllable, and “English” is English. Words that do not have the property denoted by them are called foreign-meaning, or heterologte. Obviously, all adjectives denoting properties that cannot be applied to words will be heterological.
This division of adjectives into two groups seems clear and unobjectionable. It can be extended to nouns: “word” is a word, “noun” is a noun, but “clock” is not a clock and “verb” is not a verb.
A paradox arises as soon as the question is asked: to which of the two groups does the adjective “heterological” itself belong? If it is autologous, it has the property it denotes and must be heterological. If it is heterological, it does not have the property it calls and must therefore be autological. There is a paradox.

By analogy with this paradox, it is easy to formulate other paradoxes of the same structure. For example, is someone who kills every non-suicidal person and does not kill any suicide person commit suicide or not?

It turned out that Grellig's paradox was known back in the Middle Ages as the antinomy of an expression that does not name itself. One can imagine the attitude towards sophisms and paradoxes in modern times if a problem that required an answer and caused lively debate was suddenly forgotten and was rediscovered only five hundred years later!

Another, apparently simple antinomy was indicated at the very beginning of our century by D. Berry.

The set of natural numbers is infinite. The set of those names for these numbers that are, for example, in the Russian language and contain less than, say, a hundred words, is finite. This means that there are such natural numbers for which there are no names in Russian that consist of less than a hundred words. Among these numbers there is obviously the smallest number. It cannot be called by means of a Russian expression containing less than a hundred words. But the expression: “The smallest natural number, for which its complex name does not exist in Russian, consisting of less than a hundred words” is just the name of this number! This name has just been formulated in Russian and contains only nineteen words. An obvious paradox: the named number turned out to be the one for which there is no name!

§ 4. Insoluble dispute

One famous paradox is based on a seemingly small incident that happened more than two thousand years ago and has not been forgotten to this day.

The famous sophist Protagoras, who lived in the 5th century. BC, there was a student named Euathlus, who studied law. According to the agreement concluded between them, Evatl had to pay for training only if he won his first trial. If he loses this process, he is not obliged to pay at all. However, after completing his studies, Evatl did not participate in the processes. This lasted quite a long time, the teacher’s patience ran out, and he sued his student. Thus, for Euathlus this was the first process. Protagoras justified his demand as follows:

“Whatever the court’s decision, Evatl will have to pay me.” He will either win this first trial or lose. If he wins, he will pay according to our agreement. If he loses, he will pay according to this decision.

Euathlus appears to have been a capable student, since he replied to Protagoras:

- Indeed, I will either win the trial or lose it. If I win, the court's decision will release me from the obligation to pay. If the court's decision is not in my favor, it means I lost my first case and will not pay due to our agreement.

Solutions to the Protagoras and Euathlus paradox

Puzzled by this turn of events, Protagoras devoted a special essay to this dispute with Euathlus, “The Litigation for Payment.” Unfortunately, it, like most of what Protagoras wrote, has not reached us. Nevertheless, we must pay tribute to Protagoras, who immediately sensed a problem behind a simple judicial incident that deserved special study.

G. Leibniz, himself a lawyer by training, also took this dispute seriously. In his doctoral dissertation, "A Study of Intricate Cases in Law," he tried to prove that all cases, even the most intricate ones, like the litigation of Protagoras and Euathlus, must find a correct solution on the basis of common sense. According to Leibniz, the court should refuse Protagoras for untimely filing of the claim, but should, however, retain the right to demand payment of money from Euathlus later, namely after the first case he won.

Many other solutions to this paradox have been proposed.

They referred, in particular, to the fact that a court decision should have greater force than a private agreement between two persons. To this we can answer that without this agreement, no matter how insignificant it may seem, there would have been neither a court nor its decision. After all, the court must make its decision precisely about it and on its basis.

They also turned to the general principle that all work, and therefore the work of Protagoras, must be paid. But it is known that this principle has always had exceptions, especially in a slave-owning society. Moreover, it is simply not applicable to the specific situation of the dispute: after all, Protagoras, while guaranteeing a high level of training, himself refused to accept payment if his student failed in the first process.

Sometimes they argue like this. Both Protagoras and Euathlus are both partially right, and neither of them is right in general. Each of them takes into account only half of the possibilities that are beneficial to themselves. Full or comprehensive consideration opens up four possibilities, of which only half are beneficial to one of the disputants. Which of these possibilities is realized will be decided not by logic, but by life. If the verdict of the judges has greater force than the contract, Euathlus will have to pay only if he loses the case, i.e. by virtue of a court decision. If the private agreement is placed higher than the decision of the judges, then Protagoras will receive payment only if Euathlus loses the case, i.e. by virtue of an agreement with Protagoras. This appeal to life completely confuses everything. What, if not logic, can judges be guided by in conditions when all relevant circumstances are completely clear? And what kind of leadership will it be if Protagoras, who claims payment through the court, achieves it only by losing the process?

However, Leibniz’s solution, which at first seems convincing, is slightly better than the unclear opposition of logic and life. In essence, Leibniz proposes to retroactively replace the wording of the contract and stipulate that the first trial involving Euathlus, the outcome of which will decide the issue of payment, should not be the trial of Protagoras. This thought is profound, but not related to a specific court. If there had been such a clause in the original agreement, there would have been no need for litigation at all.

If by the solution to this difficulty we mean the answer to the question whether Euathlus should pay Protagoras or not, then all these, like all other conceivable solutions, are, of course, untenable. They represent nothing more than a departure from the essence of the dispute; they are, so to speak, sophistical tricks and tricks in a hopeless and insoluble situation. For neither common sense, nor any general principles concerning social relations are capable of resolving the dispute.
It is impossible to execute together a contract in its original form and a court decision, whatever the latter may be. To prove this, simple means of logic are sufficient. Using these same means, it can also be shown that the contract, despite its completely innocent appearance, is internally contradictory. It requires the implementation of a logically impossible proposition: Evatl must simultaneously pay for training and at the same time not pay.

Rules that lead to dead ends

It is, of course, difficult for the human mind, accustomed not only to its strength, but also to its flexibility and even resourcefulness, to come to terms with this absolute hopelessness and admit that it is driven into a dead end. This is especially difficult when the deadlock situation is created by the mind itself: it, so to speak, stumbles out of the blue and ends up in its own networks. And yet we have to admit that sometimes, and however, not so rarely, agreements and systems of rules, formed spontaneously or introduced deliberately, lead to insoluble, hopeless situations.

An example from recent chess life will once again confirm this idea.

International rules for chess competitions oblige chess players to record the game move by move clearly and legibly. Until recently, the rules also stated that a chess player who, due to lack of time, missed recording several moves must, “as soon as his time trouble ends, immediately fill out his form, recording the missed moves.” Based on this instruction, one judge at the 1980 Chess Olympiad (Malta) interrupted a game under severe time pressure and stopped the clock, declaring that the control moves had been made and, therefore, it was time to put the records of the games in order.

“But excuse me,” cried the participant, who was on the verge of losing and counting only on the intensity of passions at the end of the game, “after all, not a single flag has fallen yet and no one can ever (this is also written in the rules) tell how many moves have been made.”
The judge was supported, however, by the chief arbiter, who stated that, indeed, since the time trouble was over, it was necessary, following the letter of the rules, to begin recording the missed moves.
There was no point in arguing in this situation: the rules themselves led to a dead end. All that remained was to change their wording so that similar cases could not arise in the future.
This was done at the congress of the International Chess Federation, which was taking place at the same time: instead of the words “as soon as the time pressure ends,” the rules now read: “as soon as the flag indicates the end of time.”
This example clearly shows how to act in deadlock situations. It is useless to argue about which side is right: the dispute is insoluble, and there will be no winner. All that remains is to come to terms with the present and take care of the future. To do this, you need to reformulate the original agreements or rules so that they do not lead anyone else into the same hopeless situation.
Of course, such a course of action is not a solution to an insoluble dispute or a way out of a hopeless situation. It is rather a stop in front of an insurmountable obstacle and a road around it.

Paradox “Crocodile and Mother”

In Ancient Greece, the story of the crocodile and the mother, which coincides in its logical content with the paradox of “Protagoras and Eubatlus,” was very popular.
A crocodile snatched her child from an Egyptian woman standing on the river bank. To her plea to return the child, the crocodile, shedding, as always, a crocodile tear, answered:

“Your misfortune has touched me, and I will give you a chance to get your child back.” Guess whether I'll give it to you or not. If you answer correctly, I will return the child. If you don't guess, I won't give it away.

After thinking, the mother replied:

- You won't give me the child.

“You won’t get it,” concluded the crocodile. “You either told the truth or you didn’t tell the truth.” If it is true that I will not give the child away, I will not give him away, since otherwise what is said will not be true. If what was said is not true, then you did not guess correctly, and I will not give up the child by agreement.

However, the mother did not find this reasoning convincing.

“But if I told the truth, then you will give me the child, as we agreed.” If I didn’t guess that you won’t give up the child, then you must give it to me, otherwise what I said will not be untrue.

Who is right: the mother or the crocodile? What does the promise he makes oblige the crocodile to? To give the child away or, on the contrary, not to give him away? And to both at the same time. This promise is internally contradictory, and thus it is not fulfilled by the laws of logic.
The missionary ended up with the cannibals and arrived just in time for lunch. They allow him to choose in what form he will be eaten. To do this, he must utter some statement with the condition that if this statement turns out to be true, they will boil him, and if it turns out to be false, they will fry him.

What should you tell the missionary?

Of course he must say, “You will roast me.”

If he is really fried, it will turn out that he spoke the truth, and that means he must be boiled. If he is boiled, his statement will be false, and he should just be fried. The cannibals will have no choice: from “fry” comes “cook,” and vice versa.

This episode with the cunning missionary is, of course, another paraphrase of the dispute between Protagoras and Euathlus.

Sancho Panza's paradox

One old paradox, known back in Ancient Greece, is played out in “Don Quixote” by M. Cervantes. Sancho Panza became governor of the island of Barataria and administers court.
The first to come to him is a visitor and says: “Sir, a certain estate is divided into two halves by a high-water river... So, there is a bridge across this river, and right there on the edge there is a gallows and there is something like a court, in which there is usually Four judges sit, and they judge on the basis of the law issued by the owner of the river, the bridge and the entire estate, which law is drawn up in this way: “Everyone passing over the bridge over this river must declare under oath: where and why he is going, and whoever tells the truth, let those through, and those who lie, without any leniency, send them to the gallows located right there and execute them.” From the time when this law in all its severity was promulgated, many managed to cross the bridge, and as soon as the judges were satisfied that the passers-by were telling the truth, they let them through. But then one day a certain man, sworn in, swore and said: he swears that he came to be hanged on this very gallows, and for nothing else. This oath perplexed the judges, and they said: “If we allow this man to continue unhindered, it will mean that he has violated the oath and, according to the law, is guilty of death; if we hang him, then he swore that he came only to be hanged on this gallows, therefore, his oath, it turns out, is not false, and on the basis of the same law he should be let through.” And so I ask you, Señor Governor, what should the judges do with this man, because they are still perplexed and hesitant...
Sancho suggested, perhaps not without cunning: let the half of the person who told the truth be let through, and the half who lied should be hanged, and thus the rules for crossing the bridge will be respected in full. This passage is interesting in several ways.
First of all, it is a clear illustration of the fact that the hopeless situation described in the paradox may well be encountered—and not in pure theory, but in practice—if not by a real person, then at least by a literary hero.

The solution proposed by Sancho Panza was, of course, not a solution to the paradox. But this was precisely the solution that only remained to be resorted to in his situation.
Once upon a time, Alexander the Great, instead of untying the tricky Gordian knot, which no one had ever managed to do, simply cut it. Sancho did the same. There was no point in trying to solve the puzzle on its own terms; it was simply unsolvable. All that remained was to discard these conditions and introduce our own.
And one moment. With this episode, Cervantes clearly condemns the exorbitantly formal scale of medieval justice, permeated with the spirit of scholastic logic. But how widespread in his time - and this was about four hundred years ago - was information from the field of logic! Not only Cervantes himself is aware of this paradox. The writer finds it possible to attribute to his hero, an illiterate peasant, the ability to understand that he is faced with an insoluble task!

§ 5. Other paradoxes

The above paradoxes are arguments that result in a contradiction. But there are other types of paradoxes in logic. They also point out some difficulties and problems, but they do this in a less harsh and uncompromising form. These, in particular, are the paradoxes discussed below.

Paradoxes of imprecise concepts

Most concepts not only in natural language, but also in the language of science are imprecise, or, as they are also called, vague. This often turns out to be the cause of misunderstandings, disputes, and even simply leads to deadlock situations.
If the concept is imprecise, the boundary of the area of ​​objects to which it is applied is lacking in sharpness and blurred. Take, for example, the concept of “heap”. One grain (grain of sand, stone, etc.) is not a heap. A thousand grains is obviously a heap. What about three grains? How about ten? With the addition of how many grains does a heap form? Not very clear. Just as it is not clear with the removal of which grain the heap disappears.
The empirical characteristics “large”, “heavy”, “narrow”, etc. are inaccurate. Common concepts such as “sage”, “horse”, “house”, etc. are inaccurate.
There is not a grain of sand which, when removed, we can say that once it is removed, what remains can no longer be called home. But this seems to mean that at no point in the gradual dismantling of the house - right up to its complete disappearance - is there any basis for declaring that the house does not exist! The conclusion is clearly paradoxical and discouraging.
It is easy to see that the reasoning about the impossibility of forming a heap is carried out using the well-known method of mathematical induction. One grain does not form a heap. If n grains do not form heaps, then n+1 grains do not form heaps. Therefore, no number of grains can form a heap.
The possibility of this and similar proofs leading to absurd conclusions means that the principle of mathematical induction has a limited scope. It should not be used in reasoning with imprecise, vague concepts.

A good example of how these concepts can lead to irresolvable disputes is a curious trial that took place in 1927 in the United States. The sculptor C. Brancusi went to court demanding that his works be recognized as works of art. Among the works sent to New York for the exhibition was the sculpture "Bird", which is now considered a classic of the abstract style. It is a modulated column of polished bronze about one and a half meters high, which does not have any external resemblance to a bird. Customs officers categorically refused to recognize Brancusi's abstract creations works of art. They put them under "Metal hospital utensils and household items" and imposed a heavy customs duty on them. Outraged, Brancusi filed a lawsuit.

Customs was supported by artists - members of the National Academy, who defended traditional methods in art. They acted as witnesses for the defense at the trial and categorically insisted that the attempt to pass off the “Bird” as a work of art was simply a scam.
This conflict vividly emphasizes the difficulty of operating with the concept of “work of art”. Sculpture is traditionally considered a type visual arts. But the degree of similarity of a sculptural image to the original can vary within very wide limits. And at what point does a sculptural image, increasingly moving away from the original, cease to be a work of art and become a “metal utensil”? This question is as difficult to answer as the question of where the border is between a house and its ruins, between a horse with a tail and a horse without a tail, etc. By the way, modernists are generally convinced that sculpture is an object of expressive form and it does not have to be an image.

Handling imprecise concepts thus requires a certain amount of caution. Isn't it better then to abandon them altogether?

The German philosopher E. Husserl was inclined to demand from knowledge such extreme rigor and accuracy that is not found even in mathematics. In this regard, Husserl's biographers ironically recall an incident that happened to him in childhood. He was given a penknife, and, deciding to make the blade extremely sharp, he sharpened it until there was nothing left of the blade.
More precise concepts are preferable to imprecise ones in many situations. The usual desire to clarify the concepts used is quite justified. But it must, of course, have its limits. Even in the language of science, a significant part of the concepts is imprecise. And this is not due to the subjective and random mistakes of individual scientists, but to the very nature of scientific knowledge. In natural language, the vast majority of imprecise concepts; this speaks, among other things, of his flexibility and hidden strength. Anyone who demands extreme precision from all concepts risks being left without a language altogether. “Deprive words of all ambiguity, all uncertainty,” wrote the French esthetician J. Joubert, “turn them... into single digits - play will leave speech, and with it eloquence and poetry: everything that is mobile and changeable in affections soul, will not be able to find its expression. But what am I saying: deprive... I will say more. Deprive a word of any imprecision, and you will even be deprived of axioms.”
For a long time, both logicians and mathematicians did not pay attention to the difficulties associated with vague concepts and their corresponding sets. The question was posed like this: concepts must be precise, and everything vague is unworthy of serious interest. In recent decades, however, this overly strict attitude has lost its appeal. Logical theories have been constructed that specifically take into account the uniqueness of reasoning with imprecise concepts.
The mathematical theory of the so-called fuzzy sets, indistinctly defined collections of objects, is actively developing.
The analysis of problems of inaccuracy is a step towards bringing logic closer to the practice of ordinary thinking. And we can assume that it will bring many more interesting results.

Paradoxes of inductive logic

There is, perhaps, no section of logic that does not have its own paradoxes.
Inductive logic has its own paradoxes, which have been actively, but so far without much success, being fought for almost half a century. Of particular interest is the confirmation paradox discovered by the American philosopher K. Hempel. It is natural to consider that general propositions, in particular scientific laws, are confirmed by their positive examples. If we consider, say, the statement “All A's are B,” then its positive examples will be objects that have properties A and B. In particular, the supporting examples for the statement “All crows are black” are objects that are both ravens and black. This statement is equivalent, however, to the statement “All things that are not black are not crows,” and the confirmation of the latter must also be a confirmation of the former. But “Everything that is not black is not a crow” is confirmed by every case of a non-black object that is not a crow. It turns out, therefore, that the observations “The cow is white”, “The shoes are brown”, etc. confirm the statement “All crows are black.”

An unexpected paradoxical result follows from seemingly innocent premises.

In the logic of norms, a number of its laws cause concern. When they are formulated in meaningful terms, their inconsistency with ordinary ideas about what is proper and what is prohibited becomes obvious. For example, one of the laws says that from the order “Send a letter!” the order “Send the letter or burn it!” follows.
Another law states that if a person has violated one of his duties, he gets the right to do whatever he wants. Our logical intuition does not want to come to terms with this kind of “laws of necessity”.
In the logic of knowledge, the paradox of logical omniscience is intensively discussed. He claims that a person knows all the logical consequences arising from the positions he accepts. For example, if a person knows the five postulates of Euclid’s geometry, then he knows all this geometry, since it follows from them. But that's not true. A person may agree with the postulates and at the same time not be able to prove the Pythagorean theorem and therefore doubt that it is true at all.

§ 6. What is a logical paradox

There is no exhaustive list of logical paradoxes, nor is it possible.
The paradoxes discussed are only a part of all those discovered to date. It is likely that many other paradoxes, and even completely new types of them, will be discovered in the future. The concept of paradox itself is not so defined that it would be possible to compile a list of at least already known paradoxes.
“Set-theoretic paradoxes are a very serious problem, not for mathematics, however, but rather for logic and the theory of knowledge,” writes the Austrian mathematician and logician K. Gödel. “The logic is consistent. There are no logical paradoxes,” says mathematician D. Bochvar. These kinds of discrepancies are sometimes significant, sometimes verbal. The point largely depends on what exactly is meant by a logical paradox.

The uniqueness of logical paradoxes

A logical dictionary is considered a necessary feature of logical paradoxes.
Paradoxes classified as logical must be formulated in logical terms. However, in logic there are no clear criteria for dividing terms into logical and non-logical. Logic, which deals with the correctness of reasoning, seeks to reduce the concepts on which the correctness of practically applied conclusions depends to a minimum. But this minimum is not predetermined unambiguously. In addition, non-logical statements can be formulated in logical terms. Whether a particular paradox uses only purely logical premises is not always possible to determine unambiguously.
Logical paradoxes are not strictly separated from all other paradoxes, just as the latter are not clearly distinguished from everything that is non-paradoxical and consistent with prevailing ideas. At the beginning of the study of logical paradoxes, it seemed that they could be identified by the violation of some, not yet studied, provision or rule of logic. The principle of a vicious circle introduced by B. Russell especially actively claimed the role of such a rule. This principle states that a collection of objects cannot contain members definable only by that same collection.
All paradoxes have one common property - self-applicability, or circularity. In each of them, the object in question is characterized by a certain set of objects to which it itself belongs. If we single out, for example, the most cunning person, we do this with the help of a set of people, which includes this person. And if we say: “This statement is false,” we characterize the statement in question by reference to the set of all false statements that includes it.

In all paradoxes, the self-applicability of concepts takes place, which means that there is, as it were, a movement in a circle, ultimately leading to the starting point. In an effort to characterize an object of interest to us, we turn to the totality of objects that includes it. However, it turns out that for its definiteness it itself needs the object in question and cannot be clearly understood without it. In this circle, perhaps, lies the source of paradoxes.
The situation is complicated, however, by the fact that such a circle is present in many completely non-paradoxical arguments. Circular is a huge variety of the most ordinary, harmless and at the same time convenient ways expressions. Examples such as “the largest of all cities”, “the smallest of all natural numbers”, “one of the electrons of the iron atom”, etc., show that not every case of self-applicability leads to a contradiction and that it is important not only in ordinary language, but also in the language of science.
Mere reference to the use of self-applying concepts is therefore not sufficient to discredit paradoxes. Some additional criterion is needed to separate self-applicability, leading to a paradox, from all its other cases.
There were many proposals on this matter, but a successful clarification of circularity was never found. It turned out to be impossible to characterize circularity in such a way that every circular reasoning leads to a paradox, and every paradox is the result of some circular reasoning.
An attempt to find some specific principle of logic, the violation of which would be distinctive feature all logical paradoxes, did not lead to anything definite.
Undoubtedly, some classification of paradoxes would be useful, dividing them into types and types, grouping some paradoxes and contrasting them with others. However, nothing lasting was achieved in this matter either.

The English logician F. Ramsay, who died in 1930, when he was not yet twenty-seven years old, proposed dividing all paradoxes into syntactic and semantic. The first includes, for example, Russell’s paradox, the second includes the “Liar”, Grelling, etc. paradoxes.
According to Ramsey, the paradoxes of the first group contain only concepts belonging to logic or mathematics. The latter include such concepts as “truth”, “definability”, “naming”, “language”, which are not strictly mathematical, but rather related to linguistics or even the theory of knowledge. Semantic paradoxes seem to owe their appearance not to some error in logic, but to the vagueness or ambiguity of some non-logical concepts, therefore the problems they pose concern language and must be solved by linguistics.

It seemed to Ramsey that mathematicians and logicians had no need to be interested in semantic paradoxes. Later it turned out, however, that some of the most significant results of modern logic were obtained precisely in connection with a more in-depth study of precisely these non-logical paradoxes.
The division of paradoxes proposed by Ramsey was widely used at first and retains some significance today. At the same time, it is becoming increasingly clear that this division is rather vague and relies primarily on examples rather than on an in-depth comparative analysis of the two groups of paradoxes. Semantic concepts have now received precise definitions, and it's hard not to admit that these concepts really belong to logic. With the development of semantics, which defines its basic concepts in terms of set theory, the distinction made by Ramsey becomes increasingly blurred.

Paradoxes and Modern Logic

What conclusions for logic follow from the existence of paradoxes?
First of all, the presence of a large number of paradoxes speaks of the strength of logic as a science, and not of its weakness, as it might seem.

It is no coincidence that the discovery of paradoxes coincided with the period of the most intensive development of modern logic and its greatest successes.
The first paradoxes were discovered even before the emergence of logic as a special science. Many paradoxes were discovered in the Middle Ages. Later, however, they turned out to be forgotten and were rediscovered already in our century.
Medieval logicians were not aware of the concepts of “set” and “element of a set,” which were introduced into science only in the second half of the 19th century. But the sense for paradoxes was so honed in the Middle Ages that already at that time certain concerns were expressed about self-applicable concepts. The simplest example is the concept of “being one's own element,” which appears in many of the current paradoxes.
However, such concerns, like all warnings regarding paradoxes in general, were not sufficiently systematic and definite until our century. They did not lead to any clear proposals for a revision of habitual ways of thinking and expression.
Only modern logic has brought the very problem of paradoxes out of oblivion and discovered or rediscovered most of the specific logical paradoxes. She further showed that the methods of thinking traditionally studied by logic are completely insufficient for eliminating paradoxes, and indicated fundamentally new methods for dealing with them.
Paradoxes pose an important question: where, in fact, do some conventional methods of concept formation and methods of reasoning fail us? After all, they seemed completely natural and convincing, until it turned out that they were paradoxical.

Paradoxes undermine the belief that the usual methods of theoretical thinking by themselves and without any special control over them provide reliable progress towards the truth.
Demanding a radical change in an overly credulous approach to theorizing, paradoxes represent a sharp critique of logic in its naive, intuitive form. They play the role of a factor that controls and sets restrictions on the way of constructing deductive systems of logic. And this role can be compared with the role of an experiment that tests the correctness of hypotheses in sciences such as physics and chemistry, and forces changes to be made to these hypotheses.
A paradox in a theory speaks of the incompatibility of the assumptions underlying it. It acts as a timely detected symptom of the disease, without which it could have been overlooked.
Of course, the disease manifests itself in a variety of ways, and in the end it can be revealed without such acute symptoms as paradoxes. Let's say, the foundations of set theory would have been analyzed and clarified even if no paradoxes had been discovered in this area. But there would not have been the sharpness and urgency with which the paradoxes discovered in it posed the problem of revising set theory.

An extensive literature is devoted to paradoxes, and a large number of explanations have been proposed. But none of these explanations is generally accepted, and there is no complete agreement on the origin of paradoxes and ways to get rid of them.
“Over the past sixty years, hundreds of books and articles have been devoted to the goal of resolving paradoxes, but the results are amazingly poor in comparison with the efforts expended,” writes A. Frenkel. “It seems,” H. Curry concludes his analysis of the paradoxes, “that a complete reform of logic is required, and mathematical logic can become the main tool for carrying out this reform.”

If you are not completely confused after reading this collection, then you are not thinking clearly enough.
Since ancient times, scientists and thinkers have loved to entertain themselves and their colleagues by posing unsolvable problems and formulating various kinds of paradoxes. Some of these thought experiments remain relevant for thousands of years, which indicates the imperfections of many popular scientific models and “holes” in generally accepted theories that have long been considered fundamental. We invite you to reflect on the most interesting and surprising paradoxes, which, as they now say, “blew the minds” of more than one generation of logicians, philosophers and mathematicians.
Aporia "Achilles and the Tortoise"
The Achilles and the Tortoise Paradox is one of the aporias (logically correct but contradictory statements) formulated by the ancient Greek philosopher Zeno of Elea in the 5th century BC. Its essence is as follows: the legendary hero Achilles decided to compete in a race with a turtle. As you know, turtles are not known for their agility, so Achilles gave his opponent a head start of 500 m. When the turtle overcomes this distance, the hero sets off in pursuit at a speed 10 times greater, that is, while the turtle crawls 50 m, Achilles manages to run the 500 m handicap given to him . Then the runner overcomes the next 50 m, but at this time the turtle crawls away another 5 m, it seems that Achilles is about to catch up with her, but the rival is still ahead and while he runs 5 m, she manages to advance another half a meter and so on. The distance between them is endlessly shrinking, but in theory, the hero never manages to catch up with the slow turtle; it is not much, but is always ahead of him.


Of course, from the point of view of physics, the paradox makes no sense - if Achilles moves much faster, he will in any case get ahead, but Zeno, first of all, wanted to demonstrate with his reasoning that the idealized mathematical concepts of “point in space” and “moment of time” do not too suitable for correct application to real movement. Aporia exposes the discrepancy between the mathematically sound idea that non-zero intervals of space and time can be divided indefinitely (so the turtle must always stay ahead) and the reality in which the hero, of course, wins the race.
Time loop paradox
Paradoxes involving time travel have long been a source of inspiration for science fiction writers and creators of science fiction films and TV series. There are several options for time loop paradoxes; one of the simplest and most graphic examples of such a problem was given in his book “The New Time Travelers” by David Toomey, a professor at the University of Massachusetts.
Imagine that a time traveler bought a copy of Shakespeare's Hamlet from a bookstore. He then went to England during the time of the Virgin Queen Elizabeth I and, finding William Shakespeare, handed him the book. He rewrote it and published it as his own work. Hundreds of years pass, Hamlet is translated into dozens of languages, endlessly republished, and one of the copies ends up in that same bookstore, where a time traveler buys it and gives it to Shakespeare, who makes a copy, and so on... Who should be considered in this case? the author of an immortal tragedy?
The paradox of a girl and a boy
In probability theory, this paradox is also called "Mr. Smith's Children" or "Mrs. Smith's Problem." It was first formulated by the American mathematician Martin Gardner in one of the issues of Scientific American magazine. Scientists have been arguing over the paradox for several decades, and there are several ways to resolve it. After thinking about the problem, you can come up with your own solution.
The family has two children and it is known for sure that one of them is a boy. What is the probability that the second child is also male? At first glance, the answer is quite obvious - 50 to 50, either he really is a boy or a girl, the chances should be equal. The problem is that for two-child families, there are four possible combinations of children's sexes - two girls, two boys, an older boy and a younger girl, and vice versa - an older girl and a younger boy. The first can be excluded, since one of the children is definitely a boy, but in this case there are three possible options, not two, and the probability that the second child is also a boy is one chance out of three.
Jourdain's paradox with a card
The problem proposed by the British logician and mathematician Philippe Jourdain at the beginning of the 20th century can be considered one of the varieties of the famous liar paradox.
Imagine - you are holding a postcard in your hands, which says: "The statement on the back of the postcard is true." Turning the card over reveals the phrase “The statement on the other side is false.” As you understand, there is a contradiction: if the first statement is true, then the second is also true, but in this case the first must be false. If the first side of the postcard is false, then the phrase on the second cannot be considered true either, which means that the first statement again becomes true... Even more interesting option The liar's paradox is in the next paragraph.
Sophistry "Crocodile"
A mother and child are standing on the river bank, suddenly a crocodile swims up to them and drags the child into the water. The inconsolable mother asks to return her child, to which the crocodile replies that he agrees to give him back unharmed if the woman correctly answers his question: “Will he return her child?” It is clear that a woman has two answer options - yes or no. If she claims that the crocodile will give her the child, then everything depends on the animal - considering the answer to be true, the kidnapper will release the child, but if he says that the mother was mistaken, then she will not see the child, according to all the rules of the contract.
The woman’s negative answer complicates everything significantly - if it turns out to be correct, the kidnapper must fulfill the terms of the deal and release the child, but thus the mother’s answer will not correspond to reality. To ensure the falsity of such an answer, the crocodile needs to return the child to the mother, but this is contrary to the contract, because her mistake should leave the child with the crocodile.
It is worth noting that the deal proposed by the crocodile contains a logical contradiction, so his promise is impossible to fulfill. The author of this classic sophism is considered to be an orator, thinker and political figure Corax of Syracuse, who lived in the 5th century BC.
Aporia "Dichotomy"


Another paradox from Zeno of Elea, demonstrating the incorrectness of the idealized mathematical model movements. The problem can be put like this - let's say you set out to go through some street in your city from beginning to end. To do this, you need to overcome the first half of it, then half of the remaining half, then half of the next segment, and so on. In other words - you walk half of the entire distance, then a quarter, one eighth, one sixteenth - the number of decreasing segments of the path tends to infinity, since any remaining part can be divided in two, which means it is impossible to go the whole way. Formulating a somewhat far-fetched paradox at first glance, Zeno wanted to show that mathematical laws contradict reality, because in fact you can easily cover the entire distance without a trace.
Aporia "Flying Arrow"
The famous paradox of Zeno of Elea touches upon the deepest contradictions in the ideas of scientists about the nature of motion and time. Aporia is formulated as follows: an arrow fired from a bow remains motionless, since at any moment in time it rests without moving. If at each moment of time the arrow is at rest, then it is always at rest and does not move at all, since there is no moment in time at which the arrow moves in space.


The outstanding minds of mankind have been trying for centuries to resolve the paradox of a flying arrow, but from a logical point of view, it is absolutely correct. To refute it, it is necessary to explain how a finite time interval can consist of an infinite number of moments of time - even Aristotle, who convincingly criticized Zeno's aporia, failed to prove this. Aristotle rightly pointed out that a period of time cannot be considered the sum of some indivisible isolated moments, but many scientists believe that his approach does not differ in depth and does not refute the existence of a paradox. It is worth noting that by posing the problem of a flying arrow, Zeno did not seek to refute the possibility of movement, as such, but to reveal contradictions in idealistic mathematical concepts.
Galileo's paradox
In his Discourses and Mathematical Proofs Concerning Two New Branches of Science, Galileo Galilei proposed a paradox that demonstrates the curious properties of infinite sets. The scientist formulated two contradictory judgments. First, there are numbers that are the squares of other integers, such as 1, 9, 16, 25, 36, and so on. There are other numbers that do not have this property - 2, 3, 5, 6, 7, 8, 10 and the like. Thus, the total number of perfect squares and ordinary numbers must be greater than the number of perfect squares alone. The second proposition: for each natural number there is its exact square, and for each square there is an integer square root, that is, the number of squares is equal to the number of natural numbers.
Based on this contradiction, Galileo concluded that reasoning about the number of elements was applied only to finite sets, although later mathematicians introduced the concept of power of a set - with its help, the validity of Galileo’s second judgment was proven for infinite sets.
The Potato Bag Paradox


Let's say a certain farmer has a bag of potatoes weighing exactly 100 kg. Having examined its contents, the farmer discovers that the bag was stored in damp conditions - 99% of its mass is water and 1% other substances contained in potatoes. He decides to dry the potatoes a little so that their water content drops to 98% and moves the bag to a dry place. The next day it turns out that one liter (1 kg) of water has indeed evaporated, but the weight of the bag has decreased from 100 to 50 kg, how can this be? Let's calculate - 99% of 100 kg is 99 kg, which means the ratio of the mass of dry residue to the mass of water was initially equal to 1/99. After drying, water accounts for 98% of the total mass of the bag, which means the ratio of the mass of the dry residue to the mass of water is now 1/49. Since the mass of the residue has not changed, the remaining water weighs 49 kg.
Of course, an attentive reader will immediately discover a gross mathematical error in the calculations - the imaginary comic “sack of potatoes paradox” can be considered an excellent example of how, with the help of seemingly “logical” and “scientifically supported” reasoning, one can literally build a theory from scratch that contradicts common sense. sense.
Raven paradox
The problem is also known as Hempel's paradox - it received its second name in honor of the German mathematician Carl Gustav Hempel, the author of its classic version. The problem is formulated quite simply: every raven is black. It follows from this that anything that is not black cannot be a raven. This law is called logical contraposition, that is, if a certain premise “A” has a consequence “B”, then the negation of “B” is equivalent to the negation of “A”. If a person sees a black raven, this strengthens his belief that all ravens are black, which is quite logical, but in accordance with contraposition and the principle of induction, it is logical to state that observing objects that are not black (say, red apples) also proves that all crows are painted black. In other words, the fact that a person lives in St. Petersburg proves that he does not live in Moscow.
From a logical point of view, the paradox looks impeccable, but it contradicts real life- red apples in no way can confirm the fact that all crows are black.

In examples No. 4, 5,6, the same technique is used: different meanings, situations, themes are mixed in identical words, one of which is not equal to the other, that is, the law of identity is violated.

2. Logical paradoxes

Paradox (from the Greek unexpected, strange) is something unusual and surprising, something that diverges from usual expectations, common sense and life experience.

A logical paradox is such an unusual and surprising situation when two contradictory propositions are not only simultaneously true (which is impossible due to the logical laws of contradiction and the excluded middle), but also follow from each other and condition each other.

A paradox is an insoluble situation, a kind of mental impasse, a “stumbling block” in logic: throughout its history, many different ways to overcome and eliminate paradoxes have been proposed, but none of them is still exhaustive, final and generally accepted.

Some paradoxes (paradoxes of the “liar”, “village barber”, etc.) are also called antinomies (from the Greek: contradiction in law), that is, reasoning in which it is proven that two statements that deny each other follow from each other . It is believed that antinomies represent the most extreme form of paradoxes. However, quite often the terms “logical paradox” and “antinomy” are considered synonymous.

A separate group of paradoxes are aporia (from the Greek - difficulty, bewilderment) - reasoning that shows contradictions between what we perceive with our senses (see, hear, touch, etc.) and what can be mentally analyzed (contradictions between the visible and the imaginable).

The most famous aporia was put forward by the ancient Greek philosopher Zeno of Elea, who argued that the movement we observe everywhere cannot be made the subject of mental analysis. One of his famous aporias is called "Achilles and the Tortoise." She says that we may well see how the fleet-footed Achilles catches up and overtakes the slowly crawling turtle; However, mental analysis leads us to the unusual conclusion that Achilles can never catch up with the tortoise, although he moves 10 times faster than it. When he covers the distance to the turtle, during the same time it will cover 10 times less, namely 1/10 of the path that Achilles traveled, and this 1/10 will be ahead of him. When Achilles travels this 1/10th of the way, the turtle will cover 10 times less distance in the same time, that is, 1/100th of the way, and will be ahead of Achilles by this 1/100th. When he passes 1/100th of the path separating him and the turtle, then in the same time it will cover 1/1000th of the path, still remaining ahead of Achilles, and so on ad infinitum. We become convinced that the eyes tell us one thing, but the thought tells us something completely different (the visible is denied by the imaginable).

Logic has created many ways to resolve and overcome paradoxes. However, none of them is without objections and is not generally accepted.

2.1 Examples of logical paradoxes

The most famous logical paradox is the “liar” paradox. He is often called the “king of logical paradoxes.” It was discovered back in Ancient Greece. According to legend, the philosopher Diodorus Kronos vowed not to eat until this paradox was resolved and died of hunger, having achieved nothing. There are several different formulations of this paradox. It is most briefly and simply formulated in a situation when a person utters a simple phrase: “I am a liar.” Analysis of this statement leads to a stunning result. As you know, any statement can be true or false. Let us assume that the phrase “I am a liar” is true, that is, the person who uttered it told the truth, but in this case he is really a liar, therefore, by uttering this phrase, he lied. Let us assume that the phrase “I am a liar” is false, that is, the person who uttered it lied, but in this case he is not a liar, but a truth-teller, therefore, by uttering this phrase, he told the truth. It turns out something amazing and even impossible: if a person told the truth, then he lied; and if he lied, then he told the truth (two contradictory judgments are not only simultaneously true, but also follow from each other).

Another famous logical paradox discovered in the 20th century. English logician and philosopher Bertrand Russell, is the “village barber” paradox. Let's imagine that in a certain village there is only one barber who shaves those residents who do not shave themselves. Analysis of this simple situation leads to an extraordinary conclusion. Let's ask ourselves: can a village barber shave himself? Let us assume that the village barber shaves himself, but then he is one of those village residents who shave themselves and whom the barber does not shave, therefore, in this case he does not shave himself. Let us assume that the village barber does not shave himself, but then he is one of those village residents who do not shave themselves and whom the barber shaves, therefore, in this case, he shaves himself. It turns out incredible: if a village barber shaves himself, then he does not shave himself; and if he does not shave himself, then he shaves himself (two contradictory judgments are simultaneously true and mutually condition each other).

The Protagoras and Euathlus paradox appeared in Ancient Greece. It is based on a seemingly simple story, which is that the sophist Protagoras had a student Euathlus, who took lessons in logic and rhetoric from him. The teacher and student agreed in such a way that Euathlus would pay Protagoras a tuition fee only if he won his first trial. However, upon completion of the training, Evatl did not participate in any process and, of course, did not pay the teacher any money. Protagoras threatened him that he would sue him and then Euathlus would have to pay in any case. “You will either be sentenced to pay a fee, or you will not be sentenced,” Protagoras told him, “if you are sentenced to pay, you will have to pay according to the verdict of the court; if you are not sentenced to pay, then you, as the winner of your first trial, will have to pay according to our agreement.” To this Evatl answered him: “Everything is correct: I will either be sentenced to pay a fee, or I will not be sentenced; if I am sentenced to pay, then I, as the loser of my first lawsuit, will not pay according to our agreement; if I am not sentenced to pay, then I will not pay the court’s verdict.” Thus, the question of whether Euathlus should pay Protagoras or not is unanswerable. The contract between teacher and student, despite its completely innocent appearance, is internally, or logically, contradictory, since it requires the implementation of an impossible action: Evatl must both pay for training and not pay at the same time. Because of this, the agreement itself between Protagoras and Euathlus, as well as the question of their litigation, represents something other than a logical paradox.

Task 2

Determine the structure, type of judgment, make a symbolic relationship between terms, indicating their distribution:

"Individuals have high intellectual abilities"

1. Judgment structure:

1) Subject – “high intellectual abilities”

2) Predicate – “in individual people”

3) The ligament is expressed

4) Quantifier word “Is” (expressed)

Frequently affirmative some S is P

QS is P

2. The judgment is general in quantity and affirmative in quality

3. In an explicit logical form: “Individuals have high intellectual abilities.”

4. Formula: All S are P. Judgment – ​​A.

5. R

7. The subject is distributed, the predicate is not distributed.

10 -

“There is no such person who would not like gifts.”

1. Judgment structure:

1) Subject – “Gifts”

2) Predicate – “Man”

3) The link is expressed – which would not be liked

4) Quantifier word “Everything” (not expressed)

2. The judgment is general in quantity and generally negative in quality

3. In an explicit logical form: “All people love gifts.”

4. Formula: No S is P. Judgment – ​​E. generally negative

5. R

6. The terms are in a relationship - subordination.

7. The subject is distributed, the predicate is not distributed

11 -

Task 3

Determine the type of inference, draw a conclusion, construct an inference diagram, establish the logical consistency of the reasoning:

“A person who has committed a minor crime for the first time may be released from criminal liability, if it repented or reconciled with the victim. Ivanov is determined to either repent or reconcile with the victim, which means...”

Ivanov is determined to either repent or reconcile with the victim, which means that if he has committed a crime of minor gravity for the first time, he can be released from criminal liability.

1. Type of judgments in premises:

1st premise: “A person who has committed a crime of minor gravity for the first time may be released from criminal liability if he has repented or reconciled with the victim. Ivanov is determined to either repent or reconcile with the victim.” – an implicative-conjunctive proposition, consisting of two implications united by a conjunction.

p – a person may be exempt from criminal liability

g – it repented of what it did or it reconciled itself with the victim

q – it did not repent and did not try

2nd premise: “The person will either repent and reconcile with the victim, or not.” – a disjunctive judgment consisting of 2 alternatives.

2.Scheme of inference:

(p→g) Λ (¬p→q)

p V ¬p________________

g V q

3. Simple design dilemma

4. Conclusion: “A person who has committed a minor crime will either be released or not.”

5.References

1) Getmanova A.D. Logic textbook. M.: Vlados, 1994.

2) Gusev D.A. Textbook on logic for universities. Moscow: Unity-Dana, 2004

3) Ivin A.A. The art of thinking correctly. M.: Education, 1990.

4) Koval S. From entertainment to knowledge / Transl. O. Unguryan. Warsaw: Scientific and Technical Publishing House, 1972.