Full Idea
It would seem that the thinking part is, or most nearly is, the individual self.
Gist of Idea
It would seem that the thinking part is the individual self
Source
Aristotle (Nicomachean Ethics [c.334 BCE], 1166a25)
Book Reference
Aristotle: 'Ethics (Nicomachean)', ed/tr. ThomsonJ A K/TredennickH [Penguin 1976], p.294
A Reaction
It seems that where Socrates identifies the self with the whole of the psuché (and hence is interested in its immortality, in 'Phaedo'), Aristotle considers the self to be merely the thinking and rational part of the psuché.
Related Idea
Idea 1650 For Socrates our soul, though hard to define, is our self [Vlastos on Socrates]