III. Replies to Gettier
This is the solution that is suggested by Sober (155-6).
A theory of justification is a form of infallibilism if it entails that if a person is justified in believing something, then that thing is true. In other words, infallibilists about justification believe that in order to be justified in believing something, our evidence for it must guarantee that it is true. Recall that Gettier's argument required the assumption that it is possible to be justified in believing something that is false. The infallibilist reply to Gettier rejects this assumption.
One problem with this reply is that it seems to lead us into skepticism, since it seems to be that only on rare occasions does our evidence for some proposition guarantee that it is true.
Descartes seems to be an infallibilist about justification. We will look at his views in the next section -- in particular we'll look at how he attempts be an infallibilist while still avoiding skepticism.
B. A Causal Theory
Another possible response to Gettier's argument is to admit that his argument refutes JTB. Then we reject JTB, and instead hold a "causal" theory of knowledge (CTK):
CTK: 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, and
(iv) the fact that p caused S to believe p
CTK avoids the Gettier counterexample I presented. CTK does not imply that I know that someone in the class is from Oklahoma City, since the fact that someone in the class is from Oklahoma City is not what caused me to believe it.
But this theory may have problems of its own. It may not make sense for mathematical knowledge (such as that 2+2=4) or knowledge of analytic truths (such as that all bachelors are unmarried). Also, the lottery case (Sober, 155) may refute CTK.