Full Idea
Space is a necessary representation, a priori, which is the ground of all outer intuitions. One can never represent that there is no space, although one can very well think that there are no objects to be encountered.
Gist of Idea
Space is an a priori necessary basic intuition, as we cannot imagine its absence
Source
Immanuel Kant (Critique of Pure Reason [1781], B038/A24)
Book Reference
Kant,Immanuel: 'Critique of Pure Reason', ed/tr. Guyer,P /Wood,A W [CUO 1998], p.158
A Reaction
The proposal that space is a mental intuition rather than a reality strikes me, and most people, as daft, but the observation that we are incapable of imagining the absence of space is striking. It is one of the basics of thought.