I have in what just goes before been engaged in physical inquiries a little further than perhaps I intended. But, it being necessary to make the nature of sensation a little understood; and to make the difference between the QUALITIES in bodies, and the IDEAS produced by them in the mind, to be distinctly conceived, without which it were impossible to discourse intelligibly of them;—I hope I shall be pardoned this little excursion into natural philosophy; it being necessary in our present inquiry to distinguish the PRIMARY and REAL qualities of bodies, which are always in them (viz. solidity, extension, figure, number, and motion, or rest, and are sometimes perceived by us, viz. when the bodies they are in are big enough singly to be discerned), from those SECONDARY and IMPUTED qualities, which are but the powers of several combinations of those primary ones, when they operate without being distinctly discerned;—whereby we may also come to know what ideas are, and what are not, resemblances of something really existing in the bodies we denominate from them. 23. Three Sorts of Qualities in Bodies. The qualities, then, that are in bodies, rightly considered are of three sorts:— FIRST, The bulk, figure, number, situation, and motion or rest of their solid parts. Those are in them, whether we perceive them or not; and when they are of that size that we can discover them, we have by these an idea of the thing as it is in itself; as is plain in artificial things. These I call PRIMARY QUALITIES. SECONDLY, The power that is in any body, by reason of its insensible primary qualities, to operate after a peculiar manner on any of our senses, and thereby produce in US the different ideas of several colours, sounds, smells, tastes, &c. These are usually called SENSIBLE QUALITIES. THIRDLY, The power that is in any body, by reason of the particular constitution of its primary qualities, to make such a change in the bulk, figure, texture, and motion of ANOTHER BODY, as to make it operate on our senses differently from what it did before. Thus the sun has a power to make wax white, and fire to make lead fluid. The first of these, as has been said, I think may be properly called real, original, or primary qualities; because they are in the things themselves, whether they are perceived or not: and upon their different modifications it is that the secondary qualities depend. The other two are only powers to act differently upon other things: which powers result from the different modifications of those primary qualities. 24. The first are Resemblances; the second thought to be Resemblances, but are not, the third neither are nor are thought so.