Full Idea
The Cogito argument proves that subjective experience is the most reliable, but it makes unjustified claims about the certainty of the Self.
Gist of Idea
The Cogito proves subjective experience is basic, but makes false claims about the Self
Source
comment on René Descartes (Meditations [1641], §2.26) by Bertrand Russell - Problems of Philosophy Ch 2
Book Reference
Russell,Bertrand: 'The Problems of Philosophy' [OUP 1995], p.8