Aristotle

Aristotle (384-322 B.C.E.) was a student of Plato's who made a number of advances in the theory of knowledge.

Probably the most lasting of Aristotle's innovations is his argument in favor of what has come to be called "foundationalism," the view that there are fundamental starting points upon which all other knowledge is based. For "scientific" knowledge to be demonstrated, the premises must be primary and indemonstrable, "otherwise they will require demonstration in order to be known, since to have knowledge, if it be not accidental knowledge, of things which are demonstrable, means precisely to have a demonstration of them" (Posterior Analytics, Book I, Chapter 2).

There are two objections to this conclusion. The first claims that on Aristotle's view, scientific knowledge is impossible, on the grounds that all scientific knowledge is demonstrative, and therefore any demonstration involves an infinite regress. Aristotle agrees that an infinite chain of demonstration is impossible, but he rejects the claim that it is required for demonstration. "Our own doctrine is that not all knowledge is demonstrative: on the contrary, knowledge of the immediate premisses is independent of demonstration (the necessity of this is obvious; for since we must know the prior premises from which the demonstration is drawn, and since the regress must end in immediate truths, those truths must be indemonstrable.)" (Posterior Analytics, Book I, Chapter 3). This response does no more than re-state Aristotle's original position, but he does added that there is an "originative source" which enables us to recognize the indemonstrables.

The second objection to indemonstrables is that all scientific knowledge is demonstrable. If so, then circular reasoning is permissible, a claim to which Aristotle strongly objected. Although his objections are somewhat technical, based on the peculiarities of his theory of demonstration, The most accessible objection is that if circular reasoning is admitted, one may prove anything by the simple expedient of assuming it to be so. "The upholders of circular reasoing are in the position of saying that if A is, A must be a simple way of proving anything" (Posterior Analytics, Book I, Chapter 3).

Aside from his defense of foundationalism, Aristotle made other important contributions to the theory of knowledge, including his treatment of induction and his use of the dialectical method in philosophical theorizing.