Full Idea
I could pretend that I had no body, and that there was no world or place that I was in, but I could not, for all that, pretend that I did not exist.
Gist of Idea
I can deny my body and the world, but not my own existence
Source
René Descartes (A Discourse on Method [1637], §4.32)
Book Reference
Descartes,René: 'Discourse on Method/The Meditations', ed/tr. Sutcliffe,F.E. [Penguin 1968], p.54
A Reaction
He makes the (in my opinion) appalling blunder of thinking that because he can pretend that he has no body, that therefore he might not have one. I can pretend that gold is an unusual form of cheese. However, "I don't exist" certainly sounds wrong.