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Laws of logic

Speeches and oral presentations in the modern world are very powerful means of influencing the listener. Correct and logical speech is a very important component of the success of any speaker. The clearer what you are talking about, the higher the chance for your listeners to understand your words correctly. In order to improve his speech, to make it more accurate and more logical, the speaker must know the laws of logic. Consider them in this article.

Law of identity

The first law of logic, called the law of identity, says that any judgment must be definite, precise, clear, that is, identical with itself. For the first time this law is found in the work "Artatotle's Metaphysics". In free form, the law of identity is also reflected in everyday speech. We say that talking about everything is talking about nothing.

The logical law of identity imposes a restriction on the substitution of concepts, the use of words in different meanings. This law does not give rise to ambiguity and divergence from the topic of reasoning. In symbolic form, this law can be written as follows: a → a (If a, then a), where a denotes any statement, concept, or reasoning.

Violation of the law of identity underlies:

  • Logical errors.They arise when the law of identity is violated unknowingly, unintentionally.
  • Sophism Sophism is the correct evidence of false judgment with a conscious violation of the laws of logic. Sophisms serve to confuse the interlocutor.
  • Comic effects. They arise when different situations are described in the same words. For example, the aphorism: "Do not stand anywhere, but it will still fall."
  • Puzzles and riddles. Since childhood, we know the riddle “What did the elephant do when Napoleon came (was he on the field)?” There is an ambiguity due to the consonance of words.
  • Focuses. The focus effect is based on the difference between what the magician does and how the audience sees it.

Law of contradiction

The law of contradiction imposes a restriction on the simultaneous existence and truth of 2 opposite judgments about one object in one time interval, under the same circumstances and in one respect. In symbolic form, this law can be written as: ¬ (a Λ ¬ a), (It is not true that a and not a), where a means any statement.

Human thinking is consistent in nature, but the basic laws of logic, however, include the law of contradiction.This is due to the fact that contradictions are of different types:

  • Contact, when the logical contradiction is within a small fragment of the text. By virtue of their visibility in speech are extremely rare.
  • Distant when the original judgment and its contradiction are separated by a sufficiently large amount of text. Often found in speeches, due to non-obviousness and low visibility. Distant contradictions may be noticed by your interlocutor, if he is listening to you carefully.
  • Explicit, when judgments directly contradict each other. In speech and text are rare, because highly visible.
  • Implicit when the contradiction is only implied. Often found due to low visibility. As well as distant, implicit contradictions are noticed in the speech of listeners.
  • Imaginary, when the reasoning is constructed in such a way that it looks contradictory, although it does not contain a contradiction. For example, the phrase of Anton Chekhov about childhood: “I had no childhood as a child” is not a contradiction, since in the first case, the word “childhood” refers to the time period, and in the second - the state of the soul. Imaginary contradictions are widely used in literature as an artistic device.

The law of contradiction, by not allowing two opposite judgments to be simultaneously true, does not prohibit their simultaneous falsity, which finds wide application in ordinary life. We can characterize something with turns such as "This is not good, but not bad."

Law of the excluded middle

Sayings are not only contradictory, but also opposite. The opposite is different from contradiction in that in addition to the two opposing statements there is a third, intermediate statement. In contradiction, there is no, and there can be no intermediate statement. For example, “a tall man” and “a short man” are contradictory judgments. A "high man" and "low man" - the opposite, because there is another proposition “a man of average height”.

The third statement plays a big role: its presence in the system of opposing judgments allows them to be simultaneously false, and the absence of contradictions in the system does not allow them to be false at the same time.

For contradictions, the second law of logic is necessary, but not sufficient, since it does not prohibit the simultaneous falsity of two propositions.To resolve this situation, the law of the excluded middle was introduced, which states that the truth of one of the contradictory judgments necessarily entails the falsity of the second. This law imposes a restriction on the simultaneous existence and falsity of 2 opposite judgments about one object in one time interval, under the same circumstances and in one respect.

Law of reason

The fourth law of logic states that any thesis, in order to be valid, must have a basis by which it is proved. Such grounds should be sufficient to prove the thesis. An example of violation of a law of sufficient reason is, for example, the following phrase: “Do not give me a deuce, ask something else (thesis), because I read the entire textbook, perhaps I will answer something (basis). In this case, the thesis is not the basis, because the student could read the entire textbook, but did not understand or forget what was read.

The law of sufficient reason is the basis of the most important principle of jurisprudence - the presumption of innocence, which requires that a person be considered innocent until proven reliably by the facts of his guilt.This law plays an important role in everyday life, urging us not to take unfounded allegations. He also warns us against the dissemination of gossip, sensations and fables, does not allow us to make hasty conclusions without sufficient reason. The law of sufficient reason is one of the fundamental principles of any science.

So, within the framework of this article, we examined 4 laws of logic, which play a large role in the construction of high-quality speeches and texts.


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