I. Introduction to Epistemology

One central question in epistemology is, What is the nature of knowledge.  A proposed answer to this questions is a theory of knowledge, a statement of the necessary and sufficient conditions for knowledge, a statement of this form:

S knows that p if and only if __________.

      A. Three Kinds of Knowledge

The above question about knowledge is about propositional knowledge, not object knowledge or know-how (see Sober, pp. 150-151).

      B. Plato's Theaetetus

Theaetetus's Theory of Knowledge (TTK):

TTK: S knows that p if and only if (i) S believes that p, and (ii) p is true.

Argument against TTK (Sober, 152-153)
Imagine a person, Clyde, who comes to believe that spring will come late merely on the basis of the fact that the Official Designated Groundhog saw its own shadow on Groundhog's Day.  Suppose, just by luck, Clyde's believe happens to be true -- it really is the case that spring will come late.  None of us will want to say that Clyde knows that spring will come late.  He has no good reasons for believing it.  "There is no real connection between the groundhog seeing its shadow and the coming of a late spring" (Sober, 153).  But TTK implies that Clyde does know that spring will come late.  Therefore, TTK is false.

      C. Justification

Plato says that the missing ingredient is justification.  In order to know something, you must be justified in believing it.  You must have evidence for it.  You must have some good reason for believing it.  As Plato says, you must have "an account."