Why we can’t, ultimately, prove anything

Agrippa’s trilemma, named after one of the ancient Skeptics, clearly shows the limits of human knowledge

Gustave Doré's portrait of Baron Münchhausen, Wikimedia

Back in 1968, the German philosopher Hans Albert proposed an argument aimed at showing that certain knowledge is, ultimately, impossible.

The idea was that whenever someone wants to prove a proposition—of any kind—we can always ask for proof of how the proof itself works. It turns out that there are only three possibilities:

A circular argument: the proof is based on a proposition or set of propositions that is, in turn, ultimately based on the first proof;

A regressive argument: the proof is based on another proof, which is based on another proof, and so on ad infinitum;

A dogmatic argument: the proof is based on an axiom or assumption which is simply taken for granted for the purpose of the discussion.

Albert called this Münchausen’s trilemma, after a fictional character—the Baron Münchausen—created by the German writer Rudolf Erich Raspe and protagonist of his book, Baron Münchausen’s Narrative of his Marvelous Travels and Campaigns in Russia, published in 1785.