Full Idea
One can make a powerful case for supposing that some self-knowledge is a priori. At most, if not all, of our waking moments, each of us knows of herself that she exists.
Gist of Idea
We have some self-knowledge a priori, such as knowledge of our own existence
Source
Philip Kitcher (The Nature of Mathematical Knowledge [1984], 01.6)
Book Reference
Kitcher,Philip: 'The Nature of Mathematical Knowledge' [OUP 1984], p.29
A Reaction
This is a begrudging concession from a strong opponent to the whole notion of a priori knowledge. I suppose if you ask 'what can be known by thought alone?' then truths about thought ought to be fairly good initial candidates.