# What is Deductive Reasoning in Aristotelian Logic?

June 26, 2021 Off By Felso

Since Aristotle’s main concern was the form of proof, he was most concerned with reasoning called syllogism or syllogism (syllogism), and predicted that this could provide certain information about reality.

For example,

“All men are mortal,
Socrates is a man,
So Socrates is mortal”

in his syllogism, the conclusion is not drawn only according to the formal rules of logic; Aristotle assumed that the result was confirmed in reality. In syllogism, one reaches a specific state (e.g., “Socrates is mortal” or “It is good to help the poor”) from the universal (e.g., a principle such as “All men are mortal” or “All human actions are good”). Since Aristotle refers to categories such as “man”, “mortal” and a specific human being, “Socrates”, they are called “categorical syllogisms”.

If the placement of these terms is not perfect, then the form of the syllogism will be useless.

For example,

“All men are Mortal,
Socrates is mortal,
So Socrates is a man”

When it is said, the form of the syllogism is corrupt. Because when reasoning on the first two propositions, it follows that only Socrates is human, not mortal. Since the form of the reasoning is faulty, there is a formal error, an illogicality in the syllogism, and the syllogism is invalid, that is, the inference it leads is not “follow-up”.

Aristotle observed that there are 256 different kinds of syllogism, but only 24 of them are valid, that is, the inferences of only 24 come “following” clearly and unequivocally. In addition to deductive reasoning, according to Aristotle, there are three laws of thought that are known to be clear and precise. The first is the “principle of non-contradiction”. This law, or principle, asserts that a statement cannot be true and false at the same time. For example, one cannot logically use the phrase “It’s raining and it’s not raining”. Statements in this form are self-contradictory and can never be true. The second law is the principle of “impossibility of the third state”. This law says that a statement must be either true or false. “It’s raining or not” is an example. The reason why it is called the “impossibility of the third state” is that it is either raining or it is not; There is no third possibility or a “middle”.

The third law is the principle of identity. This principle says that everything is equal to itself. The statement “A equals A” is true without exception. As with the first two principles, one immediately grasps this principle. That is, there is an instinctive realization of the truth of the principle, quite apart from one’s knowledge of any sense-experienced facts.

Prepared by: Sociologist Ömer YILDIRIM
Source: Omer YILDIRIM’s Personal Lecture Notes. Atatürk University Sociology Department 1st Year “Introduction to Philosophy” and 2nd, 3rd, 4th Grade “History of Philosophy” Lecture Notes (Ömer YILDIRIM); Open Education Philosophy Textbook