Full Idea
Aristotle explicitly characterises akrasia cases as ones in which one acts against one's choices [prohairesis], rather than as cases in which one chooses to act against reason.
Gist of Idea
Aristotle sees akrasia as acting against what is chosen, not against reason
Source
report of Aristotle (Nicomachean Ethics [c.334 BCE], 1148a09) by Michael Frede - A Free Will 2
Book Reference
Frede,Michael: 'A Free Will' [Univ of California 2011], p.23
A Reaction
The point is that Socrates and Plato give reason top authority, and Aristotle is not undermining that. Akrasia is a mistake at a lower level. Frede's discussion is subtle!