Full Idea
We can understand thinking without imagination or sensation, as is quite clear to anyone who attends to the matter.
Gist of Idea
We can understand thinking occuring without imagination or sensation
Source
René Descartes (Principles of Philosophy [1646], I.53)
Book Reference
Descartes,René: 'Philosophical Essays and Correspondence', ed/tr. Ariew,Roger [Hackett 2000], p.245
A Reaction
We may certainly take it that Descartes means if it is understandable then it is logically possible. To believe that thinking could occur without imagination strikes me as an astonishing error. I take imagination to be more central than understanding.