Full Idea
The sceptical method would be absurd in mathematics, because nowhere in mathematics do false assertions disguise themselves and make themselves invisible.
Gist of Idea
Scepticism is absurd in maths, where there are no hidden false assertions
Source
Immanuel Kant (Critique of Pure Reason [1781], B452/A424)
Book Reference
Kant,Immanuel: 'Critique of Pure Reason', ed/tr. Guyer,P /Wood,A W [CUO 1998], p.469
A Reaction
An interesting observation. The implication I take here is that scepticism in the realm of sensation is justified, precisely because errors and illusion do occur.