In order to see an object we must be separate from it. A space must exist between us and the object. Therefore, we imagine a space around the object, and also around ourselves, because, at some stage in our mental development, we realize that we, too, are objects. Space is the medium of our relationships with the world and everything in it, but, for all of that, we do not experience it in a palpable, physical sense. We must think space into existence.