Aristotle’s Theory of Syllogism

Aristotle defines syllogism as discourse in which certain things being stated ,something other than what is stated following necessity from their being so. This is the principle of implication and Aristotle was particularly concerned that scientific discourse should proceed from one valid step to another with precision. He wanted to discover the method  that would guarantee that conclusions were rightly inferred from their premises . Th thought that it is possible through syllogism.

The syllogism represents a special form of connected language. According to Aristotle scientific demonstrations are possible because certain words stand for certain properties, qualities or characteristics of things.  Such words stand for essential properties as compared with accidental properties.  To say that a man is mortal is to describe one of his essential properties, whereas to say that he has red hair is to describe something accidental, since to be a man it is not necessary or essential that to be have red or even any hair .

But it is essential to his being a man that he be mortal ,and it is such essential properties of things that scientific propositions look for. When we ask why it is that men are mortal  a fact we already know from experience , we are asking for a scientific or technical “reason why”.  It is at this point that the specially connected language of the syllogism comes into operation, for the syllogism represents the linking of propositions about essential properties in such a way that the conclusion necessarily follows . 

And what makes the conclusion follow is that a particular term is found in both of the premises , linking these premises together so that the conclusion necessarily follows. We say first that “all animals are mortals” and next that ’ all men are animals’ and from this it follows that “all men are mortals”. The middle term here is animals and this term is linked to the predicate mortal and to the subject all men , thereby producing the implication that “all men are mortal”.  In a formal way, Aristotle sets up the structure of the syllogism as follows;

If (A) is predicated of all (B) which is a major premise; and
 (B) is predicated of all (C) which is a minor premise then
 (A) is necessarily predicated of all (C) which is conclusion; 

Aristotle’s chief interest in developing the syllogism is not simply to assure consistent reasoning but to provide an instrument for scientific demonstrations, and for this reason, again, he emphasized the relation between logic and metaphysics, between our way of knowing and what things are and how they behave. Aristotle, however, distinguished between three kinds of reasoning, each of which might use the instrument of the syllogion but with different results; these are ,first, dialectical reasoning ,which is reassuming from “opinion that are generally accepted” second, there is eristic or contentious  reassuming ,which begins with opinions that seem to be generally accepted but are really not, and, third , there is what Aristotle calls demonstrative  reasoning where the premise from which reasoning Starts are true and primary.
The value of syllogistic reasoning depended for Aristotle upon the accuracy of the premises;