For some time, the answer to this perennial question was thought by many to be “justified true belief”. If I believe X to be true, I have good reason for believing X to be true, and X really is true, then I know X. In 1963, Edmund Gettier published a now legendary three-page paper titled “Is Justified True Belief Knowledge?” in which he gave two examples of justified true belief that did not constitute knowledge. Since then, epistemologists have mostly agreed that there’s some extra ingredient requisite for knowledge but have disagreed about what it is. After drawing out Gettier’s examples, Peter Klein explains that there are two major camps. The first he calls etiology of belief: theories in which the extra ingredient has to do with how the belief was attained. Reliabilists, for example, argue that a justified true belief counts as knowledge if the belief is arrived at via a method that reliably delivers accurate beliefs. Klein belongs to the second camp: quality of evidence theories, which have to do with the strength of the justification, not the cause of the belief. Klein defends his own preferred quality of evidence theory: defeasibility theory, which involves the existence or absence of “defeaters” for the justification.
Suppose you know X. How do you know? Maybe you know because of Y. How do you know Y? Maybe the answer is Z. How do you know Z?
This is the regress problem of knowledge, also called the Agrippan trilemma and the Münchhausen trilemma. It is based on the supposition that if we claim to know something, we must have a reason for it and that reason must itself be something that we know. This leaves open four possible solutions. One is skepticism, the belief that we have no knowledge. The most common is foundationalism, which posits certain basic facts that require no external reasons to be justified. Another option is coherentism, which solves the problem via a kind of circular reasoning or justification loop. And finally, there is infinitism, the view that there is no end to the regress. For any chain of justification, the final member of the chain will always be unjustified, and it is always possible to go looking for further reasons of reasons of reasons. As infinitist Peter Klein puts it, knowledge is never “settled”. Even so, says Klein, it is still possible to have knowledge. In this interview, Klein first argues why he thinks coherentism, foundationalism, and a certain kind ofskepticism all fail. He then explains his own account of justification, as “something that we do”, and how it makes the infinitist picture look more plausible than it first seems.…
Agrippan skepticism is an ancient Greek variety. It is perhaps the hardest-hitting attack on the possibility of knowledge in the history of philosophy. I don’t know of any satisfactory solution.
Epistemologists agree on this much: in order for a belief to count as knowledge, it needs to be at least a justified true belief. What does it mean for a belief to be justified? It means we have a reason for believing it. If this reason will work as justification, it must be a reason that we know.
Of course, if we know this reason, it must be a justified true belief. So what is its justification? It has to be some other reason that we know. And we’re off on a regress.
The problem can be put this way: justification can only happen in three ways:
Regress argument: belief A is justified by belief B, which is justified by belief C, which is justified by belief D, and so on.
Circular argument: belief A is justified by belief B, which is justified by belief A.
Dogmatic argument: belief A is axiomatic. It requires no justification.
None of these options succeed in justifying a belief. Regress arguments fail to justify because they never bottom out at some belief that is already justified.…