There are certain universal truths which are self-evident, and were evolved not by experience only or argument, nor science, as they are the natural appanage of common-sense, _e.g._, such axioms as the following: the whole is greater than the part; a straight line is the shortest distance between two points; each body occupies space; every event occupies time; every effect has a cause. All these are more certain than that the sun will rise to-morrow; common-sense has always known them, and the entire human race has not waited for the coming of Kant to recognise these facts. It is strange that the majority of men who know so many things that are true by intuition, often make mistakes when they begin to reflect. They imagine that all things falling under their observation have the power of making themselves known directly, as if they entered an empty space in the imagination which was ready to receive them. Are they ignorant of the fact that in order to think of an external object, it is not necessary to have it in actuality--as it exists in nature--before one’s eyes, but that it suffices to imprint its image on the mind? This is very simple, and no doubt common-sense itself would see a truism which might be passed in silence. “What is there extraordinary,” common-sense might say, “if in thinking of a lemon, for instance, there should be at once presented to the mind a yellow fruit, of acid flavour, and of a certain shape--a lemon in fact?” This remark is useful only in showing our natural incapacity for experiencing a sensation, of whatever kind, without connecting it with an external object possessing corresponding attributes to the sensation, and which was its cause. In any case the truism is not to be ignored, since Aristotle, great philosopher as he was, did not consider it beneath his dignity to employ it. He said: “I think of a stone; the stone is not in my mind, but its form is.” To prove to common-sense that its remark has no connection with the thesis recently laid down, would serve no good purpose. A personal mental act, if it be lawful to personate a quality, would alone convince common-sense of its error; but when once convinced common-sense would then have changed to something higher than it had previously been. It will have mounted up one stage towards reason, and in following this route under the guidance of increasing reason, it will end by understanding this truth as demonstrated by Kant: he who cannot distinguish a real object from its representation will never understand the working of the human mind. The importance of this truth must excuse my digression. METAPHYSICS.