No one denies that they have some categories in common. Their relations to time are identical. Both, moreover, may have parts (for psychologists in general treat thoughts as having them); and both may be complex or simple. Both are of kinds, can be compared, added and subtracted and arranged in serial orders. All sorts of adjectives qualify our thoughts which appear incompatible with consciousness, being as such a bare diaphaneity. For instance, they are natural and easy, or laborious. They are beautiful, happy, intense, interesting, wise, idiotic, focal, marginal, insipid, confused, vague, precise, rational, casual, general, particular, and many things besides. Moreover, the chapters on 'Perception' in the psychology-books are full of facts that make for the essential homogeneity of thought with thing. How, if 'subject' and 'object' were separated 'by the whole diameter of being,' and had no attributes in common, could it be so hard to tell, in a presented and recognized material object, what part comes in through the sense-organs and what part comes 'out of one's own head'? Sensations and apperceptive ideas fuse here so intimately that you can no more tell where one begins and the other ends, than you can tell, in those cunning circular panoramas that have lately been exhibited, where the real foreground and the painted canvas join together.[20] Descartes for the first time defined thought as the absolutely unextended, and later philosophers have accepted the description as correct. But what possible meaning has it to say that, when we think of a foot-rule or a square yard, extension is not attributable to our thought? Of every extended object the _adequate_ mental picture must have all the extension of the object itself. The difference between objective and subjective extension is one of relation to a context solely. In the mind the various extents maintain no necessarily stubborn order relatively to each other, while in the physical world they bound each other stably, and, added together, make the great enveloping Unit which we believe in and call real Space. As 'outer,' they carry themselves adversely, so to speak, to one another, exclude one another and maintain their distances; while, as 'inner,' their order is loose, and they form a _durcheinander_ in which unity is lost.[21] But to argue from this that inner experience is absolutely inextensive seems to me little short of absurd. The two worlds differ, not by the presence or absence of extension, but by the relations of the extensions which in both worlds exist.