In “Defeating the Dogma of Defeasibility” Ram Neta argues against all positions defeasible. Neta’s paper, which is found in Williamson on Knowledge, is a comprehensive argument against the alleged “defeasibility” of knowledge. Neta endorses an often neglected stance on knowledge: that knowledge is not capable of being defeated by future evidence. While I cannot cover Neta’s entire argument in a blog post I will get his position on the table, explain Williamson’s response to one aspect of Neta’s thesis, explain how Neta, willingly, embraces epistemological dogmatism, and then raise a problem with Neta’s account. According to Neta knowledge is indefeasible justified true belief (IJTB):
- S knows that p = S has a justified, true belief that p, and there is no true proposition e such that the conjunction of e and S’s actual evidence set E does not constitute a justification for S to believe that p (169).
Neta defends the IJTB account of knowledge by showing it can properly handle a battery of cases where non-knowledge gets counted as knowledge. I’ll leave those details to the reader and fast-forward to a part in Neta’s paper that Williamson takes issue with.
Are there counterexamples against IJTB? One counterexample is found in Williamson (2000: 219). This counterexample involves a person putting one black and one red ball into a bag (e), making 10K draws and getting a red ball every time (e’), resulting in rationally doubting whether a black ball was really put in the bag and not just a red ball made to look black by a trick of lighting. The initial knowledge is defeated by future evidence. Thus, knowledge seems defeasible.
But, not so fast says Neta. There are many ways the additional evidence (e’) can interact with the person’s beliefs: (i) the belief that p is true is lost, (ii) some of the initial evidence for p is lost, (iii) being able to reasonably form the belief that p on the basis of one’s evidence is lost. A person might lose knowledge that p in any of these ways. This is not a problem for IJTB because, “IJTB says nothing about what would happen to our epistemic subject if she were to gain an additional bit of evidence. It says that, if S knows that p, then, for any true proposition e’, the conjunction of our subject’s actual evidence set with e’ constitutes a justification for our subject to believe that p.” (171) For Neta, infallibility entails indefeasibility because, “Knowledge…is belief that is properly based on infallible evidence (indeed, on evidence that can be known—perhaps upon reflection alone—to be infallible)” (354). This means that a subject can know p only based on infallible evidence for p.
Williamson points out a fallacy in Neta’s argument for the idea that S knows that p only when it’s based on infallible evidence for p. It’s possible to deduce, according to Neta, from the assumption that S knows p on the basis of e that e is not misleading evidence for p. This makes a disjunction hold: either the subject can know the evidence is not misleading based on some further, independent, evidence e’ or e is infallible evidence for p. According to Neta the first disjunct leads to a regress because it’s possible to know that e & e’ are not misleading with regard to p, and this can be known based on further, independent, evidence e”, and so on. Williamson counters this assumption by saying it only shows that all cases of the first disjunct cannot be true, but it is possible that some cases are true. The result is that only some of the time the second disjunct is true, namely, in cases when the first disjunct is false. This does not show that the second disjunct is true all the time because, as Neta argues, the first disjunct is always false because it generates an infinite regress. According to Williamson the following is quite possible:
S knows that e is not misleading with respect to p on the basis of evidence e’ distinct from e; e is fallible evidence for p; S does not know that e & e’ is not misleading with respect to p on the basis of evidence e” distinct from e & e’; e & e’ is infallible evidence for p. (354).
So, it’s possible for e to be fallible evidence for p, yet for S to know p on the basis of e (i.e. when e is conjoined with e’). Williamson launches his second wave of attack against the assumption of entailment between infallibility and indefeasibility. If the evidence is infallible, then it’s the case that if S knows p on the basis of e, then p is true; possessing the evidence guarantees the truth of the belief. However, according to both Neta and Williamson’s views, the subject may not (and need not) be in a position to access or reason to the truth of the belief. So, even knowing that e is infallible evidence for p, it’s not clear that this entails indefeasible justification for p. Simply knowing that e is infallible does not entail that, “the conjunction of e with anything should constitute a justification for S to believe p” (355). It seems Williamson missed Neta’s disclaimer about justification, as Neta confides:
[T]here may be examples in which S is justified in believing that p on the basis of evidence that can be expanded into something that is not a justification for S to believe that p—justification itself may be defeasible. But knowledge is not defeasible, according to the IJTB theory (180).
Neta leaves justification as an outstanding, perhaps defeasible, position to develop. Williamson’s comments do bring out a worry with Neta’s account. Neta is committed to epistemic dogmatism. In fact, he embraces dogmatism. As long as an agent maintains her current evidence for her knowledge that p, future evidence will never justify disbelief in p. Being dogmatic about belief that p is OK because there is no epistemic cost, reasons Neta. Holding p as a settled belief and continuing to believe p in the face of new evidence, as long as one does not lose one’s current evidence, allows one to rationally continue knowing that p. What does it mean to lose evidence? If a true proposition in one’s evidence set becomes false it falls out of the evidence set. Beliefs once true can become false in light of new evidence (i.e. true evidence may falsify other true evidence once added to the evidence set). This means one must account for future evidence because it can cause one to lose one’s current evidence for the belief, and may, as a result, justify disbelief in p. Unless Neta embraces a view that factivity is absolute (i.e. once true, always true), it seems a cost of Neta’s view is that it sanctions a conflict: retaining evidence allows one to keep belief irrespective of future evidence, yet one can lose one’s evidence in the face of future evidence and so future evidence can significantly impact one’s current evidence. It seems: future evidence is no big deal with respect to one’s current evidence and yet a big deal with respect to one’s current evidence. Which is it?
 All page references and quotes are from Williamson on Knowledge.