Regress argument

The regress argument (also known as the diallelus (Latin < Greek di allelon "through or by means of one another")) is a problem in epistemology and, in general, a problem in any situation where a statement has to be justified.

According to this argument, any proposition requires a justification. However, any justification itself requires support. This means that any proposition whatsoever can be endlessly (infinitely) questioned.

The argument is usually attributed to Sextus Empiricus, and has been restated by Agrippa as part of what has become known as "Agrippa's trilemma". The argument can be seen as a response to the suggestion in Plato's Theaetetus that knowledge is justified true belief.

Assuming that knowledge is justified true belief, then:

Throughout philosophic history many responses to this problem have been generated. Here, however, we present the three major counter-arguments: some statements do not need justification; the chain of reasoning loops back on itself; and the sequence never finishes.

Perhaps the chain begins with a belief that is justified, but which is not justified by another belief. Such beliefs are called basic beliefs. In this solution, which is called foundationalism, all beliefs are justified by basic beliefs. Foundationalism seeks to escape the regress argument by claiming that there are some beliefs for which it is improper to ask for a justification. (See also a priori.) This would be a claim that some things (basic beliefs) are true in and of themselves.

Foundationalism is the belief that a chain of justification begins with a belief that is justified, but which is not justified by another belief. Thus, a belief is justified if and only if:

Foundationalism can be compared to a building. Ordinary individual beliefs occupy the upper stories of the building; basic, or foundational beliefs are down in the basement, in the foundation of the building, holding everything else up. In a similar way, individual beliefs, say about economics or ethics, rest on more basic beliefs, say about the nature of human beings; and those rest on still more basic beliefs, say about the mind; and in the end the entire system rests on a set of basic beliefs which are not justified by other beliefs.

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