Space is the form or mental condition of our perception of external objects. The phenomena of the material world may vary in an infinite number of ways; but, under every variety, they retain the condition of existing in space, either as being themselves sensibly extended, or as having a local position in the sensitive organism. Without this condition, their existence at all as phenomena is inconceivable.
We may suppose the phenomena changed as we will in other respects, but we cannot suppose them to exist out of space. We may suppose any given phenomenon to be non-existent, but the non-existence of space is beyond our power of supposition. Hence space is necessarily regarded as infinite (though not positively conceived as such), for to suppose it finite is to suppose a point at which it ceases to exist.
It has thus the characteristics of universality and necessity, which appear to mark it out as a priori law or condition of the conscious mind, not as the adventitious result of any special experience. And this conclusion is confirmed by other considerations. For the consciousness of space, though accompanying the perceptions of various senses, cannot be regarded as properly the object of any one of them.
There is a visible extension given in the apprehension of space as occupied by light and colour; there is a tangible extension given in the consciousness of certain portions of the organism as occupied by tactual impressions; and there is probably a certain consciousness of locality in the exercise of the other senses. But pure space is not identical with any of these; for the blind man may form as positive a notion of it as the seeing man; and one debarred from the sensation accompanying the act of touch would not thereby lose all consciousness of space; and the same argument applies still more clearly to the other senses.
***Excerpt from Henry Longueville Mansel, B.d.. Metaphysics or the philosophy of consciousness