Agrippa's trilemma

In epistemology, the Münchhausen trilemma is a thought experiment used to demonstrate the impossibility of proving any truth, even in the fields of logic and mathematics. If it is asked how any knowledge is known to be true, proof may be provided. Yet that same question can be asked of the proof, and any subsequent proof. The Münchhausen trilemma is that there are only three options when providing proof in this situation:

The trilemma, then, is the decision among the three equally unsatisfying options.

The name Münchhausen-Trilemma was coined by the German philosopher Hans Albert in 1968 in reference to a trilemma of "dogmatism versus infinite regress versus psychologism" used by Karl Popper. It is a reference to the problem of "bootstrapping", based on the story of Baron Munchausen (in German, "Münchhausen") pulling himself and the horse on which he was sitting out of a mire by his own hair.

It is also known as Agrippa's trilemma after a similar argument by Sextus Empiricus, which was attributed to Agrippa the Skeptic by Diogenes Laërtius. Sextus' argument, however, consists of five (not three) "modes". Popper in his original 1935 publication mentions neither Sextus nor Agrippa, but attributes his trilemma to Jakob Fries.

In contemporary epistemology, advocates of coherentism are supposed to accept the "circular" horn of the trilemma; foundationalists rely on the axiomatic argument. The view that accepts infinite regress is called infinitism. Advocates of fallibilism, though, point out that while it is indeed correct that a theory cannot be proven universally true, it can be proven false (test method) or it can be deemed unnecessary (Occam's razor). Thus, conjectural theories can be held as long as they have not been refuted.

...
Wikipedia