If borders or limits are required for definition, and if space by definition cannot be anything spatial --and must therefore by definition be refused any limit or border --then we seem prima facie to confront in the problem of space an irresolvable ἀπορία. The apparent force of this problematic has once again asserted itself in a debate that has since fallen into ellipsis over at A City in Speech:
We will close at the present by highlighting that space constantly retreats to the background whenever it is involved in a question. Turn your mind now to the concept of space, and try to fix your thoughts upon it. What comes into your mind? If there are any images of objects within space itself, clear them at once, since space itself cannot be that which it contains. Clear away all materiality from the conception, and fix your gaze upon space itself. Stripped of matter, what remains? What is space?Thus does the problematic initially impinge itself upon our initial effort to in any way clarify it. But what initially, that is immediately, seems to of itself deny any resolution, often needs only enough pause to embark on a second reflection, i.e., it needs only the mediation of time; although space will refuse all shape and form, it nevertheless must permit of definition insofar as there properly belongs to it the possibility of being encountered as formless. After all, it must be admitted that space is not in the first place experienced as indefinable. The question is therefore begged:
What condition is necessary to make such an encounter of space, namely, as indefinable, possible?
The answer can be brought into relief negatively: there must be something non-spatial about our very encounter of space, something which allows us to see it at first only as a backdrop that is always already there in our encounter of any object of experience, only to allow us to see it later on as an indefinable fore-ground that vexes our attempts to think it. And indeed, in the course of this shift, space itself does not change, yet our encounter with it changes emphatically. The implication being brought into relief has now become obvious:what is capable of constituting the condition for the possibility of any such shifting encounter of space is not space itself but something outside of space itself, something which, being other than space, could not simply reside alongside of space (in just another space, as it were), but would have, at the same time as it remained outside of and beyond space, to permeate it through and through. Of course, in keeping with this a priori permeation, the positive identity of this non-spatial condition has, even in this our present musing upon the definition of space, necessarily already been mentioned. Space is not only bordered by what already permeates it; it is defined by this very coinciding permeation: space is defined by being defined already, i.e. it is defined by time.
Such an answer is in many ways a stock response. It is clearly drawn along Kantian lines, and is --like many things Kantian --easily incorporated into the System of Hegel. As Kant would have it, the pure inner intuition of time is not simply some complement to the pure outer intuition of space: time is not only inner intuition but also universal intuition. What is spatial is already temporal. What is important to see is that this universal status does not erase or correct time's designation as internal. Rather, time is universal intuition in a manner that outer intuition cannot be, and it must therefore be other than what is outer; it must be internal. Time must be internal intuition at the same time as it is universal intuition, and this alone vouchsafes its universal status. But what time is this, which would allow the intuition of time to be necessarily differentiated into what is internal and what is universal, while at and as the same time, insisting upon the necessity of their identity?