Logic, as you know, consists of assertions and conclusions. One of its main bricks - categorical syllogism - is a deduction built deductively, that is, a conclusion is drawn about a particular situation from a certain common one. It develops on the basis of two main arguments, or premises, interconnected by a common term. Since there are only two such arguments, the syllogism is called simple, and because the premises are affirmed (or denied) quite categorically, such a simple statement is called categorical. Here is the simplest example of such a conclusion. The first argument: "All men are mortal." The second argument: "Ivan is a man." Conclusion, it is a judgment, therefore, it sounds: "Ivan is mortal." As we see, the correctness or fallacy of all the premises is not considered here. We take as a given and the fact that human life is ever ending, and Ivan's belonging to the human race.
On the example of this simple inference, we can see that a simple categorical syllogism has its own structure. In any logical conclusion, the predicate (a word with a certain indefinite meaning, in our case, mortal creatures) is always wider than the subject (Ivan). Therefore, the premise containing the predicate is called large, and the one into which the subject enters is called small. These arguments are connected by the term-intermediary M (medium) - in our case these are people, a person. Therefore, in judicial practice, the analysis of logical inference must be started by finding out the place in it of the predicate and subject, as well as the presence of an intermediary between them.
In this analysis, it should be borne in mind that a simple categorical syllogism must also contain an axiom that is not expressed, but is present: everything that is affirmed or denied regarding the entire type of objects extends to each object of this type. Therefore, such a proposal would be erroneous: 1. Men become fathers. 2. Peter is a man. 3. Peter is the father. In this example, the axiom of syllogism is not observed, since paternity does not apply to all men. Therefore, when constructing conclusions, you must strictly adhere to the rules. There are only seven of them: three of them relate to terms, and four to premises.
Rule one: a simple categorical syllogism contains only three terms. Every fourth term is superfluous. Identification of different concepts entails a mistake. For example: 1. Sidorov committed theft. 2. Sidorov - a noun. 3. The noun committed theft. Here Sidorov and the noun have different meanings. Rule two: the intermediary term must be present in the premises. If the connection between the predicate and the subject cannot be established or it is unproven, then the syllogism remains shaky: 1. Some people are killers. 2. Ivan can be called some person. 3. Ivan is the killer. And finally, the third rule. If the term is not used in the argument of the predicate, but it is present in the conclusion, it will be a wrong syllogism. Examples of such a mistake can be expressed as follows: 1. Murders happen in Moscow and the region. 2. St. Petersburg is not located in the Moscow region. 3. There are no murders in St. Petersburg.
In addition to the rules of terms, the rules of the parcels must be observed. At least one of them must bear within itself a statement, because in order to affirm something, we must push off from something. If one of the arguments advanced is negation, then the conclusion should be negation. Also, in order for a simple categorical syllogism to be correct, at least one of the arguments put forward must have the general character of a categorical judgment. And the last rule of premises: if at least one of them is private, then the conclusion should be private. For example: 1. Crime must be punished (general judgment). 2. Ivanov committed a crime (specific case). 3. Ivanov must be punished.