The Münchhausen Trilemma

There are many forms of radical skepticism: skepticism of the external world, skepticism of other minds, and skepticism of rationality, to name just a few. They arrive at skepticism via different channels, some more successful than others.

Agrippan skepticism is an ancient Greek variety. It is perhaps the hardest-hitting attack on the possibility of knowledge in the history of philosophy. I don’t know of any satisfactory solution.

Epistemologists agree on this much: in order for a belief to count as knowledge, it needs to be at least a justified true belief. What does it mean for a belief to be justified? It means we have a reason for believing it. If this reason will work as justification, it must be a reason that we know.

Of course, if we know this reason, it must be a justified true belief. So what is its justification? It has to be some other reason that we know. And we’re off on a regress.

The problem can be put this way: justification can only happen in three ways:

  • Regress argument: belief A is justified by belief B, which is justified by belief C, which is justified by belief D, and so on.
  • Circular argument: belief A is justified by belief B, which is justified by belief A.
  • Dogmatic argument: belief A is axiomatic. It requires no justification.

None of these options succeed in justifying a belief. Regress arguments fail to justify because they never bottom out at some belief that is already justified.…

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