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these substances have or have not? Which is nothing else but to know what other simple ideas do or do not co-exist with those that make up that complex idea. $ 10. This, how weighty and consider
Because the able a part soever of human science, is yet connexion very narrow, and scarce any at all. The between reason whereof is, that the simple ideas, most simple
ideas is unwhereof our complex ideas of substances
known. are made up, are, for the most part, such as carry with them, in their own nature, no visible necessary connexion or inconsistency with any other simple ideas, whose co-existence with them we would inform ourselves about.
$ 11. The ideas that our complex ones Especially of substances are made up of, and about ofsecondary which our knowledge concerning sub- qualities. . stances is most employed, are those of their secondary qualities: which depending all (as has been shown) upon the primary qualities of their minute and insensible parts,-or if not upon them, upon something yet more remote from our comprehension,-it is impossible we should know which have a necessary union or inconsistency one with another: for not knowing the root they spring from, not knowing what size, figure, and texture of parts they are, on which depend, and from which result, those qualities which make our complex idea of gold; it is impossible we should know what other qualities result from, or are incompatible with, the same constitution of the insensible parts of gold, and so consequently must always co-exist with that complex idea we have of it, or else are inconsistent with it.
$ 12. Besides this ignorance of the pri- Because all mary qualities of the insensible parts of connexion bodies, on which depend all their secondary between any qualities, there is yet another and more in- secondary
and primary curable part of ignorance, which sets us qualities is more remote from a certain knowledge of undiscoverthe co-existence or in-co-existence (if I
able. may so say) of different ideas in the same subject; and that is, that there is no discoverable connexion between any secondary quality and those primary qualities which it depends on.
$ 13. That the size, figure, and motion of one body should cause a change in the size, figure, and motion of another body, is not beyond our conception: the separation of the parts of one body upon the intrusion of another, and the change from rest to motion upon impulse,—these and the like seem to have some connexion one with another. And if we knew these primary qualities of bodies, we might have reason to hope we might be able to know a great deal more of these operations of them one with another: but our minds not being able to discover any connexion betwixt these primary qualities of bodies and the sensations that are produced in us by them, we can never be able to establish certain and undoubted rules of the consequences or co-existence of any secondary qualities, though we could discover the size, figure, or motion of those invisible parts which immediately produce them. We are so far from knowing what figure, size, or motion of parts produce a yellow colour, a sweet taste, or a sharp sound, that we can by no means conceive how any size, figure, or motion of any particles, can possibly produce in us the idea of any colour, taste, or sound whatsoever; there is no conceivable connexion betwixt the one and the other.
$ 14.. In vain, therefore, shall we endeavour to discover by our ideas (the only true way of certain and universal knowledge) what other ideas are to be found constantly joined with that of our complex idea of any substance : since we neither know the real constitution of the minute parts on which their qualities do depend; nor, did we know them, could we discover any necessary connexion between them and any of the secondary qualities : which is necessary to be done before we can certainly know their necessary co-existence. So that let our complex idea of any species of substances be what it will, we can hardly, from the simple ideas contained in it, certainly determine the
necessary co-existence of any other quality whatso
Our knowledge in all these inquiries reaches very
little farther than our experience. Indeed, some few of the primary qualities have a necessary dependence and visible connexion one with another, as figure necessarily supposes extension ; receiving or communicating motion by impulse, supposes solidity. But though these and perhaps some other of our ideas have, yet
there are so few of them that have a visible connexion one with another, that we can by intuition or demonstration discover the co-existence of very few of the qualities are to be found united in substances : and we are left only to the assistance of our senses, to make known to us what qualities they contain. For of all the qualities that are co-existent in any subject, without this dependence and evident connexion of their ideas one with another, we cannot know certainly any two to co-exist any farther than experience, by our senses, informs us. Thus though we see the yellow colour, and upon trial find the weight, malleableness, fusibility, and fixedness, that are united in a piece of gold; yet because no one of these ideas has any evident dependence, or necessary connexion with the other, we cannot certainly know, that where any four of these are, the fifth will be there also, how highly probable soever it may be ; because the highest probability amounts not to certainty, without which there can be no true knowledge. For this co-existence can be no farther known than it is perceived ; and it cannot be perceived but either in particular subjects, by the observation of our senses, or, in general, by the necessary connexion of the ideas themselves.
$ 15. As to the incompatibility or repugnancy to co-existence, we may know nancy to cothat any subject may have of each sort of exist, larger. primary qualities but one particular at once; v. c. each particular extension, figure, number of parts, motion, excludes all other of each kind. The like also is certain of all sensible ideas peculiar to each
sense; for whatever of each kind is present in any subject, excludes all other of that sort; v. g. no one subject can have two smells or two colours at the same time. To this perhaps will be said, Has not an opal, or the infusion of lignum nephriticum, two colours at the same time? To which I answer, that these bodies, to eyes differently placed, may at the same time afford different colours; but I take liberty also to say, that, to eyes differently placed, it is different parts of the object that reflect the particles of light; and therefore it is not the same part of the object, and so not the very same subject, which at the same time appears both yellow and azure. For it is as impossible that the very same particle of any body should at the same time differently modify or reflect the rays of light, as that it should have two different figures and textures at the same time. Of the co
$ 16. But as to the powers of substances existence of to change the sensible qualities of other powers, a bodies, which make a great part of our
inquiries about them, and is no inconsiderway.
able branch of our knowledge; I doubt, as to these, whether our knowledge reaches much farther than our experience; or whether we can come to the discovery of most of these powers, and be certain that they are in any subject, by the connexion with any of those ideas which to us make its essènce. Because the active and passive powers of bodies, and their ways of operating, consisting in a texture and motion of parts, which we cannot by any means come to discover; it is but in very few cases we can be able to perceive their dependence on, or repugnance to, any of those ideas which make our complex one of that sort of things. I haye here instanced in the corpuscularian hypothesis, as that which is thought to. go farthest in an intelligible explication of those qualities of bodies; and I fear the weakness of human understanding is scarce able to substitute another, which will afford us a fuller and clearer discovery of
the necessary connexion and co-existence of the powers which are to be observed united in several sorts of them. This at least is certain, that whichever hypothesis be clearest and truest, (for of that it is not my business to determine) our knowledge concerning corporeal substances will be very little advanced by any of them, till we are made to see what qualities and powers of bodies have a necessary connexion or repugnancy one with another; which in the present state of philosophy, I think, we know but to a very small degree: and I doubt whether, with those faculties we have, we shall ever be able to carry our general knowledge (I say not particular experience) in this part much farther. Experience is that which in this part we must depend on. And it were to be wished that it were more improved. We find the advantages some men's generous pains have this way brought to the stock of natural knowledge. And if others, especially the philosophers by fire, who pretend to it, had been so wary in their observations, and sincere in their reports, as those who call themselves philosophers ought to have been, our acquaintance with the bodies here about us, and our insight into their powers and operations, had been yet much greater.
$ 17. If we are at a loss in respect of Of spirits, the powers and operations of bodies, I yet narthink it is easy to conclude, we are much more in the dark in reference to the spirits; whereof we naturally have no ideas but what we draw from that of our own, by reflecting on the operations of our own souls within us, as far as they can come within our observation. But how inconsiderable a rank the spirits that inhabit our bodies hold amongst those various and possibly innumerable kinds of nobler beings; and how far short they come of the endowments and perfections of cherubim and seraphim, and infinite sorts of spirits above us; is what by a