Full Idea
The causes of our belief in a proposition are indeed irrelevant to the question of what we believe.
Gist of Idea
Causes of beliefs are irrelevant to their contents
Source
Ludwig Wittgenstein (Zettel [1950], i.437)
Book Reference
Dennett,Daniel C.: 'Elbow Room - Free will worth wanting' [MIT 1999], p.27
A Reaction
This should have nipped the causal theory of knowledge in the bud before it got started. Everyone has a different cause for their belief that 'it sometimes rains'. Cause is not justification.