The fact that any given justification of knowledge will itself depend on another belief for its justification appears to lead to an infinite regress.
Skepticism begins with the apparent impossibility of completing this infinite chain of reasoning, and argues that, ultimately, no beliefs are justified and therefore no one really knows anything.
Fallibilism also claims that absolute certainty about knowledge is impossible, or at least that all claims to knowledge could, in principle, be mistaken. Unlike Skepticism, however, Fallibilism does not imply the need to abandon our knowledge, just to recognize that, because empirical knowledge can be revised by further observation, any of the things we take as knowledge might possibly turn out to be false.
In response to this regress problem, various schools of thought have arisen:
Foundationalism claims that some beliefs that support other beliefs are foundational and do not themselves require justification by other beliefs (self-justifying or infallible beliefs or those based on perception or certain a priori considerations).
Instrumentalism is the methodological view that concepts and theories are merely useful instruments, and their worth is measured by how effective they are in explaining and predicting phenomena. Instrumentalism therefore denies that theories are truth-evaluable. Pragmatism is a similar concept, which holds that something is true only insofar as it works and has practical consequences.
Infinitism typically takes the infinite series to be merely potential, and an individual need only have the ability to bring forth the relevant reasons when the need arises. Therefore, unlike most traditional theories of justification, Infinitism considers an infinite regress to be a valid justification.
Coherentism holds that an individual belief is justified circularly by the way it fits together (coheres) with the rest of the belief system of which it is a part, so that the regress does not proceed according to a pattern of linear justification.
Foundherentism is another position which is meant to be a unification of foundationalism and coherentism.