In all sorts of contexts, we find ourselves making distinctions between things that fit into different categories. We judge things as good or bad, true or false, justified or unjustified, beautiful or ugly, etc. In order to make such decisions, it seems that we must be using some sort of criteria: one or more rules for deciding which way to classify something. Taking the example most relevant to us here, namely the question of when beliefs are justified and so can count as knowledge, I might declare the some belief is justified if it meets the criteria of having sufficient evidence in its favour, without having any significant counterevidence. Whatever criteria I use exactly, however, it seems that I could be asked “how did you decide upon these criteria?” I am thereby called upon to give the criteria that I used for selecting the very criteria that I used to make the original judgement. However, as soon as I answer this question, I can be asked yet again “but how did you decide upon those criteria? So the process can continue indefinitely.
Another way of phrasing this problem considers the two questions: “what do we know?” and “what criteria do we use to decide whether we know something?”. We usually like to think that we make decisions on the basis of some reasons and principles, rather than merely deciding on a whim for no particular reason. This means that we need some criteria for decision making. However, it seems that we would first need to know what we know, before we are able to outline the methods we use in coming to know these things. After all, how could we possibly develop criteria without being able to check that the criteria yields correct answers in known cases of knowledge? According to the argument, therefore, we have a vicious circle: we need criteria before we can have knowledge, but we need knowledge in order to establish the criteria.
The broad notion of setting criteria has many applications. Disagreements about judgements of truth, goodness, usefuless, beauty, etc are common, and often people attempt to resolve them by appealing to some criteria. The problem is, however, that this only pushes the dispute back one step, for now there will likely be disagreement about the criteria that have been used. The problem of the criterion asks where ultimately do we get our criteria for making these sorts of judgments, and how can we justify any choices of criteria we might make? Much philosophical discussion has yielded little in the way of agreement, and there do not seem to be any easy answers to this problem.
The problem of the criterion: in-depth Internet Encyclopedia of Philosophy article covering the problem
Roderick Chisholm and the problem of the criterion: useful introductory piece explaining the problem
Outline of Chisholm’s ‘the problem of the criterion’: a stepwise summary outline of Chisholm’s argument