Let me not be misunderstood. Let me not be supposed to be courting collision with the Berkleian thesis of the non-existence of abstract ideas. I do not for one moment doubt that all our general or class notions of sensible objects or events are merely concrete ideas of individual objects or events--that, for instance, whenever we talk of man or motion in general, we are really thinking of some particular man or motion, which, as possessing all properties common to all men or motions, serves as a representative of the entire _genus_. Neither am I prepared to deny, although scarcely either prepared to admit, that even of abstract qualities all our general or class notions are equally ideas of particular specimens of those qualities; that, when we speak, for instance, of virtue or vice in general, we are thinking of some particular exhibition of some particular kind of virtue or vice. Nay, I am not even concerned to deny that our idea of idea in general may possibly be a copy of some particular one of our previous ideas which, for the nonce, serves to represent all our other previous ideas. I limit myself to saying that our idea of idea in general, whether it be or be not itself an abstraction, is, at all events, not a copy of sensation. I admit that it thereby differs essentially from most, if not all, other general ideas. Possibly it may be only through my having myself felt the promptings of some particular virtue or vice, that I am able to form an idea of that particular virtue or vice. If so, I admit that my idea of that particular virtue or vice is but, as Hume would say, a copy of my feeling. And since, undoubtedly, I can feel myself thinking, or perceiving, or performing any other mental operation, I am bound to admit, further, that my idea of any such operation may equally be described as a copy of a sensation which I have experienced. All I contend for is that if, after having formed my idea, either of a mental operation or of anything else whatever, I proceed to ask myself what sort of an entity that idea is, the answer which I give myself, or, in other words, the idea which I form of my previous idea, being a copy of idea, cannot be a copy of sensation.