Full Idea
It has been widely supposed that externalism, which holds that the contents of a person's propositional attitudes are partly determined by factors of which the person may be ignorant, cannot be reconciled with first-person authority.
Gist of Idea
It is widely supposed that externalism cannot be reconciled with first-person authority
Source
Donald Davidson (Epistemology Externalized [1990], p.197)
Book Reference
Davidson,Donald: 'Subjective, Intersubjective, Objective' [OUP 2001], p.197
A Reaction
It is certainly a bit puzzling if you go around saying 'Actually, people don't know their own thoughts'. Davidson aims to defend first-person authority. The full story is developed in Tyler Burge's views on 'anti-individualism'.