Full Idea
Surely whether I am asleep or awake, two plus three makes five, and a square does not have more than four sides.
Gist of Idea
Surely maths is true even if I am dreaming?
Source
René Descartes (Meditations [1641], §1.20)
Book Reference
Descartes,René: 'Discourse on Method/The Meditations', ed/tr. Sutcliffe,F.E. [Penguin 1968], p.98