Proof of this proposition can only be given in the same way as of any other ultimate truth, by making trial of it; if you doubt it you may be challenged to perform the experiment of thinking of anything whatever, no matter what, as real, and then explaining what you mean by its reality. Thus suppose you say “I can think of A as real,” A being any thing in the universe; now think, as you always can, of an imaginary or unreal A, and then try to state the difference between the A which is thought of as real and the A which is thought of as merely imaginary. As Kant proved, in the famous case of the real and the imagined hundred dollars, the difference does not lie in any of the qualities or properties of the two A’s; the qualities of the imagined hundred dollars are precisely the same as those of the real sum, only that they are “imaginary.” Like the real dollars, the imagined dollars are thought of as possessing such and such a size, shape, and weight; stamped with such and such an effigy and inscription; containing such and such a proportion of silver to alloy; having such and such a purchasing power in the present condition of the market, and so forth. The only difference is that the real dollars are, or under specified and known conditions may be, the objects of direct perception, while the imaginary ones, because imaginary, cannot be given in direct perception. You cannot see or handle them; you can only imagine yourself doing so. It is in this connection with immediate psychical fact that the reality of the real coins lies. So with any other instance of the same experiment. Show me, we might say, anything which you regard as real,—no matter what it is, a stone wall, an æsthetic effect, a moral virtue,—and I will ask you to think of an unreal and imaginary counterpart of that same thing, and will undertake to prove to you that what makes the difference between the reality and the imagination is always that the real thing is indissolubly connected with the psychical life of a sentient subject, and, as so connected, is psychical matter of fact.