Full Idea
Remove from your experiential concept of a body everything empirical (colour, hardness etc), and there still remains its space. If you remove all the properties which experience teaches you, there remains substance. This shows your a priori faculty.
Gist of Idea
Experienceless bodies have space; propertyless bodies have substance; this must be seen a priori
Source
Immanuel Kant (Critique of Pure Reason [1781], B006)
Book Reference
Kant,Immanuel: 'Critique of Pure Reason', ed/tr. Guyer,P /Wood,A W [CUO 1998], p.138
A Reaction
Presumably you can also 'remove' the space and the substance. Maybe there are no actual items such as spaces or substances, so getting both of them wrong wouldn't be a good advertisement for the faculty. It's just imagination?