As coisas que se aprendem com teoria da argumentação

The Münchhausen Trilemma (after Baron Münchhausen, who allegedly pulled himself out of a swamp by his own hair), also called Agrippa's Trilemma (after Agrippa the Skeptic), is a philosophical term coined to stress the purported impossibility to prove any truth even in the fields of logic and mathematics. It is the name of an argument in the theory of knowledge going back to the German philosopher Hans Albert, and, more traditionally, Agrippa.

http://en.wikipedia.org/wiki/Münchhausen_Trilemma