The concept of a basic belief is key to foundationalism. Foundationalists hold that there are basic beliefs that are non-inferentially justified. These beliefs are supposed to halt the regress of justification, and act as the ultimate source of justification for everything else that we believe. Some critics of foundationalism, however, have argued that the idea of a basic belief makes no sense.

For a belief to be justified, there must be some reason to think that it is true; this is what justification is all about. Basic beliefs, therefore, as they are justified, must possess some feature that makes them likely to be true.

For a person to be justified in accepting a belief, they must have access to this reason. It is not enough to justify a belief that there is a good reason for thinking it true; the believer must know that there is a good reason for thinking that the belief is true. For a basic belief to be justified, therefore, the believer must know that the belief possesses this feature, and that this feature increases the likelihood that the belief is true.

In that case, though, the belief would not be basic, for it would be inferentially justified by the further beliefs that it possesses this feature and that beliefs that possess this feature are likely to be true. The regress of justification that basic beliefs were supposed to haly, then, would recommence.

If this is correct, and there can be no basic beliefs, then foundationalism must be rejected.