Full Idea
The fundamental tenet of rationalism is that thought is an independent source of knowledge.
Gist of Idea
The main claim of rationalism is that thought is an independent source of knowledge
Source
A.J. Ayer (Language,Truth and Logic [1936], Ch.4)
Book Reference
Ayer,A.J.: 'Language, Truth and Logic' [Penguin 1974], p.98
A Reaction
Presumably one should add that thought gives synthetic knowledge. Thought is also an experience, so empiricists will always acknowledge that we could have some knowledge (of thought) by thought alone.