Full Idea
This power of imagination which is in me, in so far as it differs from the power of conceiving, is in no way necessary to my nature or essence.
Gist of Idea
Imagination and sensation are non-essential to mind
Source
René Descartes (Meditations [1641], §6.73)
Book Reference
Descartes,René: 'Discourse on Method/The Meditations', ed/tr. Sutcliffe,F.E. [Penguin 1968], p.151
A Reaction
This is my candidate for the biggest blunder ever made by a great philosopher. But it was thanks to his mistake that I began to realise how totally central imagination is to the very act of thinking. Thank you, René.