The truth is that if the thinking principle is extended we neither know its form nor its seat; whilst if unextended, it is absurd to speak of its having any space-relations at all. Space-relations we shall see hereafter to be _sensible_ things. The only objects that can have mutual relations of position are objects that are perceived coexisting in the same felt space. A thing not perceived at all, such as the inextended soul must be, cannot coexist with any perceived objects in this way. No lines can be felt stretching from it to the other objects. It can form no terminus to any space-interval. It can therefore in no intelligible sense enjoy position. Its relations cannot be spatial, but must be exclusively cognitive or dynamic, as we have seen. So far as they are dynamic, to talk of the soul being 'present' is only a figure of speech. Hamilton's doctrine that the soul is present to the whole body is at any rate false: for cognitively its presence extends far beyond the body, and dynamically it does not extend beyond the brain.[210] THE RELATIONS OF MINDS TO OTHER OBJECTS are either relations to _other minds_, or to _material things_. The material things are either the mind's _own brain_, on the one hand, or _anything else_, on the other. The relations of a mind to its own brain are of a unique and utterly mysterious sort; we discussed them in the last two chapters, and can add nothing to that account. The mind's relations to other objects than the brain are _cognitive and emotional_ relations exclusively, so far as we know. It _knows_ them, and it inwardly _welcomes or rejects_ them, but it has no other dealings with them. When it seems to _act_ upon them, it only does so through the intermediary of its own body, so that not it but the body is what acts on them, and the brain must first act upon the body. The same is true when other things seem to act on it--they only act on the body, and through that on its brain.[211] All that it _can_ do _directly_ is to know other things, misknow or ignore them, and to find that they interest it, in this fashion or in that. Now the _relation of knowing_ is the most mysterious thing in the world. If we ask how one thing _can_ know another we are led into the heart of _Erkenntnisstheorie_ and metaphysics. The psychologist, for his part, does not consider the matter so curiously as this. Finding a world before him which he cannot but believe that _he_ knows, and setting himself to study his own past thoughts, or someone else's thoughts, of what he believes to be that same world; he cannot but conclude that those other thoughts know it after their fashion even as he knows it after his. Knowledge becomes for him an ultimate relation that must be admitted, whether it be explained or not, just like difference or resemblance, which no one seeks to explain.