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as really it is. Certainty of knowledge is to perceive the agreement or disagreement of ideas, as expresied in any propofition. This we usually call knowing, or being certain of the truth of any propofition. ý 4. No Proposition can be known to be true, where
the Elence of each Species mentioned is not known. Now because we cannot be certain of the truth of any general proposition, unless we know the precise buunds and extent of the species its terms stund for, it is necessary we should know the essence of each Species, which is that which constitutes and bounds it. This in all simple ideas and modes is not hard to do ; for in these the real and nominal essence being the same, or, which is all one, the abstract idea which the genesal term stands for, being the sole eflence and boune dary that is or can be supposed of the species, there can be no doubt how far the Species extends, or what things are comprehended under each term ; which, it is evident, are all that have an exact conformity with the idea it ftands for, and no other. But in substances wherein a real essence distinct from the nominal is supposed to constitute, determine, and bound the species, the extent of the general word is very uncertain ; because not knowing this real es. fence, we cannot know what is or is not of that species, and consequently what may or may not with certainty be affirmed of it. And thus speaking of a man or gold, or any other species of natural substances, as supposed constituted by a precise real eflence, which nature regularly imparts to every individual of that kind, whereby it is made to be of that species, we cannot be certain of the truth of any affirmation or negation made of it: For man or gold taken in this sense, and used for species of things constituted by real essences different from the complex idea in the mind of the speaker, stand for we know not what ; and the extent of these species, with such boundaries, are so unknown and undetermined, that it is impose fible with any certainty to afirm, that all men are ra. tional, or that all gold is yellow. But where the nee
minal: eflence is kept to, as the boundary of each species, and men extend the application of any general term no farther than to the particular things in which the complex idea it stands for is to be found, there they are in no danger to mistake the bounds of each Species, nor can be in doubt, on this account, whether any proposition be true or no. I have chose to explain this uncertainty of propositions in this scholastic way, and have inade use of the terms of elences and Species, on purpose to show the absurdity and inconve. nience there is to think of them, as of any other fort of realities, than barely abstract ideas with names to them. To suppose that the species of things are any thing but the forting of them under general names, according as they agree to several abstract ideas, of which we make those names the signs, is to confound truth, and introduce uncertainty into all general propositions that can be made about them. Though therefore these things might, to people not possesed with scholastic learning, be perhaps treated of in a better and clearer way, yet those wrong notions of efences or species having got root in most people's minds, who have received any tincture from the learning which has prevailed in this part of the world, are to be discovered and removed, to make way for that use of words which should convey certainty with it.
$ 5. This imore particularly concerns Substances. The names of fubstances then, whenever made to stand for species, which are supposed to be constituted by real efences, which we know not, are not capable to convey certainty to the understanding. Of the truth of general propositions made up of such terms, we cannot be sure; the reason whereof is plain ; for how can we be sure that this or that quality is in gold, when we know not what is or is not gold? Since in this way of speaking, nothing is gold but what partakes of an eflence, which we not knowing, cannot know where it is or is not, and so cannot be sure that any parcel of matter in the world is or is not in this sense gold ; being incurably ignorant, whether it has or has not that which makes any thing to be called geld, i. e. that real essence of gold whereof we have no idea at all: this being as impossible for us to know, as it is for a blind man to tell in what flower the colour of a panse is or is not to be found, whilst he has no idea of the colour of a panze at all. Or if we could (which is impossible certainly know where a real ellence, which we know not, is ; v.g. in what par. cels of matter the real essence of gold is ; yet could we not be sure, that this or that quality could with truth be affirmed of gold ; since it is impoflible for us to know, that this or that quality or idea has a neces. sary connection with a real essence, of which we have no idea at all, whatever species that supposed real es. sence may be imagined to constitute. Ø 6. The Truth of few universal Propofitions con
cerning Substances is to be known. On the other side, the names of substances, when made use of, as they should be, for the ideas men have in their minds, though they carry a clear and determinate signification with them, will n't yet serve us to make many universal propositions, of whose truth we can be cirtain ; not because in this use of them we are uncertain what things are signified by them, but because the complex ideas they stand for, are such combinations of simple ones, as carry not with them any discoverable connection or repugnancy, but with a very few other ideus. 5 Because co-existence of Ideas in few cases is ta
be known. The complex ideas, that our names of the species of substances properly stand for, are collections of such qualities as have been observed to co-exist in an unknown fubftraium, which we call substance : but what other qualities necessarily co-exist with such combinations, we cannot certainly know, unless we can dilcover their natural dependence ; which in their pri. mary qualities, we can go but a very little way in ; and in all their secondary qualities, we can discover no connection at all, for the reasons mentioned, chap. 3. viz. 1. Because we know not the real constitutions of substances, on which each focondary quality particularly depends. 2. Did we know that, it would serve us only for experimeutal (not universal) knowledge, and reach with certainty no farther than that bare instance ; because our understandings can discover no conceivable connection between any secondary quality, and any modification whatsoever of any of the primary ones. And therefore there are very few general propositions to be made concerning substances, which can carry with them undoubted certainty.
$ 8. Instance in Gold. ALL gold is fixed, is a proposition whose truth we cannot be certain of, how universally soever it bo believed. For if, according to the useless imagination of the schools, any one supposes the term gold to stand for a species of things set out by nature, by a real essence belonging to it, it is evident he knows not what particular substances are of that species ; and so cannot, with certainty, affirm any thing univer. sally of gold. But if he makes gold land for a species determined by its nominal effence, let the nominal es. sence, for example, be the complex idea of a body of a certain yellow colour, malleable, fusible, and beavier than any other known; in this proper use of the word gold, there is no difficulty to know what is or is not guld. But yet no other quality can with cere tainty be universally affirmed or denied of gold, but what hath a discoverable connection or inconsistency with that nominal effence. Fixedness, for example, having no necessary conve&tion, that we can discover, with the colour, weight, or any other simple idea of our complex one, or with the whole combination together, it is impoflible that we should certainly know the truth of this proposition, that all go!d is fixed.
As there is no discoverable connection between fixed. ness, and the colour, weight, and other simple ideus of that nominal eflence of gold; so if we make our complex idea of gold, a body yellow, fusible, du Etile,
weighty, and fixed, we shall be at the same uncertainty concerning solubility in aqua regia, and for the same reason ; since we can never, from consideration of the ideas themselves, with certainty affirm or deny of a body, whose complex idra is made up of yellow, very weighty, dudile, fusible, and fixed, that it is soluble in aqua regia, and so on of the rest of its qualities. I would gladly meet with one general affirmation concerning any quality of gold, that any one can certainly know is true. It will, no doubt, be presently objected, is not this an universal certain propofition, all gold is malleable ? To which I answer, it is a very certain propofition, if malleableness be a part of the complex idea the word gold stands for. But then here is nothing affirmed of gold, but that that found stands for an idea in which malleableness is contained : and such a sort of truth and certainty as this, it is to say a centaur is four-footed. But if malleablenefs makes not a part of the specific effence the name gold stands for, it is plain, all gold is malleable, is not a certain propofition ; because, let the complex idea of gold be made up of which foever of its other qualities you please, malleableness will not appear to de. pend on that complex idea, nor follow from any fimple one contained in it; the coonection that malleablone/shas (if it has any) with those other qualities, being only by the intervention of the real constitution of its insensible parts ; which, since we know not, it is imporlible we should perceive that connection, unless we could discover that which ties then together. § 10. As far as any fucb co-existence can be known,
so far universal Propositions may be certain. But
this will go but a little way, because, The more, indeed, of these co-existing qualities we unite into one complex idea, under one name, the more precise and determinate we make the significa. tion of that word; but yet never make it thereby more capable of universal certainty, in respect of other qualities not contained in our complex idea, fince we perceive not their connection or dependence one on