Syllogism

Syllogism

A syllogism is described as mediate inference and deductive inference and also as confined to propositions which express the relation of attribute to substance.

A syllogism is a rhetorical device that starts an argument with a reference to something general and from this it draws conclusion about something more specific. Syllogism takes the form of Enthymeme; an argument in which one premise is not explicitly stated.

Syllogism may also be used to form incorrect conclusions that are odd. For instance, “Some televisions are black and white and all penguins are black and white. Therefore, some televisions are penguins” This is a  false argument as it implies a conclusion “all black birds are crows” is incorrect. It is known as Syllogism Fallacy. This conclusion is practically impossible.

For example: the arguments

a.       If A=B

B=C

Then A=C is mediate  but not deductive

b.      All the same circle in which AB, AC, AD of circle BCD are equal; is deductive but not mediate.

c.       All men are mortal.

Rahim is a man.

So Rahim is mortal; both deductive.

Valid mode of syllogism

Aristotle and other traditional logicians provided certain rules which determine the validity of syllogism. Here are some rules to check the validity of syllogism.

-          Avoid four terms: fallacy of four terms, a formal mistake in which a categorical syllogism contains more than three terms.

Example: all men are rational animal. All chalks are white. Therefore, -----.

A valid standard form categorical syllogism must contain  exactly three terms, each of which is used in the same sense throughout the argument. If there are more times than, it cannot be in a standard form syllogism, we cannot call it syllogism.

-          The middle term must be distributed at least once: the middle term is what connects the major and the minor term. If the middle term is never distributed, then the major and minor terms might be related to different parts of the M class, thus giving no common ground to relate S  and P.

-          If a term is distributed in the conclusion, then it must be distributed in a premise: when a term is distributed in the conclusion, let’s say the P is distributed, then that term is saying something about every member of the P class. If the same term is  not distributed in the major premise, then the major premise is saying something about only some member of the P class. Minor premise says nothing about the P class. Therefore, the conclusion contains information that is not contained in the premises, making the argument invalid.

-          No conclusion drawn from two negative premises: if the premises are both negative, the relationship between S and P is denied. The conclusion cannot, therefore, say anything is a positive fashion.

-          Any syllogism having exactly one negative statement is invalid: which means a negative premise requires a negative conclusion and a negative conclusion requires a negative premise.

-          If both premises are universal, the conclusion cannot be particular. And also there is no conclusion from two particular premises.