Students of Kant have known, in a general way, that he attributed "extension" to "bodies," as derived by them from _a priori_ mind. _Space_ is so derived; hence all things _in_ space, which is the "form," the "condition" of their existence, must partake of its nature, which is pure extension, pure "given quantity," as he designates it. But why does the _shape_ of a material body belong to "pure intuition," and _come from mind_? Simply because the shape (let it be of a stone) is merely the _objected_ "_synthesis of apprehension_," in which the properties of the stone, as impressions of sense, are _unified_, but in accordance with their special variety. The shape is their "figurative synthesis," their "_synthesis speciosa_." Now, in the meaning of Kant, and in the nature of the case, space is _made_ in precisely the same _manner_ as a stone; only the stone is full of diverse properties--special effects on sense, got from some impinging background of matter--some "noumenon"--while space has no properties at all, except additions and divisions of _itself_--spaces. In other words, the stone is a _special_ relation between mental synthesis and sensuous susceptibility, the latter being in particular impact with some noumenal non-ego, and being definitely _filled_ from it. Space, on the other hand, is a _general_ relation between the same mental synthesis and the same sensuous susceptibility, the latter holding _no contents_ from any noumenon, yet being recipient to _all_ possibility of noumenal impact. Hence, space is just "the synthesis of apprehension" itself, set in self-reflex, objected, phenomenated. The stone, in its unity, its form, its "shape," is this objected synthesis of apprehension, _filled_ with certain sensuous effects. The synthesis of apprehension, again, as the condition of any special "shape" into which it may be stuffed, is of course _a priori_ to _the_ stuffed shape; so space is _a priori_ to the stone in space. Once again, space is the outward representation, the very double to the eye, of the synthesis of apprehension; for space is just the _visible synthesis of the apprehended_--the transparent base of co-existence for all external things. It must be remembered that the synthesis of apprehension, as the "mind" of "sense," is itself a _double_, containing the pure conjunctive unity of "unconscious understanding" as an active factor, and susceptibility to impact as a passive factor. In the conjoined relation of these two factors every material phenomenon gets to exist; so there must be _some_ relation of space to _every_ external object, and to _all_ external objects--which is to say at once that space is _infinite_, both in extent and divisibility, so far as it can apply to objects _at all_.