Aristotle's Logic

The History of Western Philosophy
Bertrand Russell

Ch. XXII Aristotle's Logic

Aristotle's influence was large in general. It was largest in the field of logic. "Even
at the present day, all Catholic teachers of philosophy and many others still obstinately reject the
discoveries of modern logic, and adhere with a strange tenacity to a system which is as definitely
antiquated as Ptolemaic astronomy" (Russell, 195).

Aristotle's most important work in the field of logic is the syllogism, an argument made up of major premise, a minor premise and a conclusion.

If Aristotle's logic had been the beginning of logic and not the end, it would be easy to estimate it as historically important. But, because it was adhered to for thousands of years as the totality of logic it has some deficiencies: formal defects in the system, an over-estimation of the value of the syllogism and the over-estimation of deduction.

The formal defects in the system arise when the particulars and universals are blurred. Aristotle's system allows a lot of things to be assumed that are not necessarily true.

There are other forms of deduction and the syllogism has no priority over any other deductive argument.

All the important inferences outside logic and pure mathematics are inductive, not deductive; the only exceptions are law and theology, each of which derives its first principles from an unquestionable text, viz. the statute books or the scriptures" (Russell, 199). Even though Aristotle allowed for the importance of induction in his writing, his followers did not often mention it and thus, caused errors by accepting premises as being self-evident when they were in fact inductive in nature. Thus, if the premise is arrived at through inductive reasoning it is probably true rather than absolutely true. Two absolutely true premises lead to an absolutely true conclusion. But, if the premises are probably true than the conclusion must be probably true as well. You can see where the errors come from.

Aristotle had ten categories: substance, quantity, quality, relation, place, time, position, state, action and affection. Russell states that the definition of categories is muddy and he says that their use in philosophy is not useful.

Aristotle described a definition as a statement of a thing's essential nature, its essence. Russell argues that a thing does not have an essence, only a word can have an essence.

Russell also attacks the Aristotelian doctrine of substance, stating that a substance is merely a collective name for a number of events. By defining those events as a substance philosophy has made a bunch of metaphysical mistakes.

"I conclude that the Aristotelian doctrines with which we have been concerned in this chapter are
wholly false, with the exception of the formal theory of the syllogism, which is unimportant" (Russell, 202).