Space is essentially one; the manifold in it, and therefore the general concept of spaces, depends solely on the introduction of limitations(kA25)
In order that certain sensations be referred to something outside me the representation of space must be presupposed(kB38)
We can never represent the absence of space to ourselves(kB39)
No concept can be thought as containing an infinite number of representations within itself, so space is an a priori intuition(kB40)
With the sole exception of space there is no subjective representation which could be entitled at once objective and a priori(kB44)
Neither space nor any a priori geometrical determination of it is a transcendental representation, what alone can be titled transcendental is the knowledge that the representations of space are not of empirical origin and the possibility that they can yet relate a priori to objects and experience(kA56)
To regard space and time as relations abstracted from experience we must deny that a priori mathematical doctrines have any validity in respect of real things(kB57)
If we regard space and time as properties which must be found in themselves, then we have two infinite things, which are not substances, yet must have existence, nay, must be the necessary condition of the existence of all things and must continue to exist even all existing things be removed(kB70)
Space and time contain a priori the condition of the possibility of objects as appearance and the synthesis which takes place in them has objective validity(kB122)
Space is merely a pure form of the appearances of outer sense(kB156)
The proof of an empty space or an empty time can never be derived from experience(kB214)
Void space is not for us an object of any possible experience(kB261)
A community of substances is utterly inconceivable as arising simply from their existence. We can however render the possibility of community- of substances as appearances- perfectly comprehensible, if we represent them to ourselves in space, that is, in outer intuition(kB294)