Full Idea
The leading claim of proponents of the a priori is that sources of justification are of two significantly different types: experiential and nonexperiential. Initially this difference is marked at the phenomenological level.
Gist of Idea
The main claim of defenders of the a priori is that some justifications are non-experiential
Source
Albert Casullo (A Priori Knowledge [2002], 5)
Book Reference
'Oxford Handbook of Epistemology', ed/tr. Moser, Paul K. [OUP 2002], p.135
A Reaction
He cites Plantinga and Bealer for the phenomenological starting point (that some knowledge just seems rationally obvious, certain, and perhaps necessary).