Some info about Plato:

Plato (428-347 BC)
- The best known ancient Greek philosopher
- Student of Socrates; teacher of Aristotle
- Wrote about 23 philosophical dialogues
- Famous doctrines: the Theory of the Forms; the Immortality of the Soul; Knowledge is Justified True Belief
- Western philosophy "consists of a series of footnotes to Plato." - A. N. Whitehead (1929)

II. The JTB Theory

For centuries upon centuries, philosophers accepted Plato's theory of knowledge, the view that knowledge is justified true belief.  This view is also known as the JTB theory.  Here is the official statement of the JTB theory:

JTB: S knows that p if and only if

(i) S believes that p, and
(ii) p is true, and
(iii) S is justified in believing that p.

Even if we accept the JTB theory, there is still a lot of work to be done in epistemology.  One major question needing attention is, What is the nature of epistemic justification?  That is, what exactly does clause (iii) of JTB mean?  An attempted answer to this questions is called a theory of justification, a statement of this form:

S is justified in believing that p if and only if __________.

Even if JTB is true, we won't really know the nature of knowledge until we also have a theory of justification.

      A. Gettier Counterexamples to JTB

In 1963, Edmund Gettier, a professor in the philosophy department here at UMass, presented strong arguments against JTB, which had been accepted for ages.  Sober presents some Gettier-style counterexamples to JTB.  Here is the one I presented in class.

Suppose I see Caleb's driver's license and it says he is from Oklahoma City.  I come to believe that

      (1) Caleb is from Oklahoma City.

It seems to me that I am justified in believing that Caleb from Oklahoma City.  For the sake of the example, let us suppose that I am.  (If you don't think I am, we could change the specifics of the example to ensure this, and Gettier's argument would still go through.)

Suppose I infer from (1) that

      (2) Someone in my class is from Oklahoma City.

Certainly, if I am justified in believing (1) and I deduce (2) from (1), then I am justified in believing (2).

Now, suppose that Caleb's ID was a fake. He's not really from Oklahoma City.  Clearly, I don't know (1), since it's not even true (though I was still justified in believing it -- justification does not require truth).  So far so good for JTB, since JTB yields the correct result here -- namely, that I don't know (1).

It also seems that I don't know (2), either, since I inferred it from (1).

But suppose finally that, unbeknownst to me, someone else in the class is, just by luck, really from Oklahoma City.  That is, just by luck, (2) is true. Now, we agreed that I don't in fact know (2).  But the thing is, I have a justified true belief that (2).  So here is a case in which I have justified true belief without knowledge.  Since JTB says that anytime someone has a justified true belief that p, he thereby knows that p, JTB is proven to be false.

We could make Gettier's counterexample into a little argument, as follows:

A Gettier-style Argument against JTB
1. If JTB is true, then I know that someone in my class is from Oklahoma City.
2. I don't know that someone in my class is from Oklahoma City.
3. Therefore, JTB is not true.

Be sure you can explain why each of the premises in this argument is true.