An Essay Concerning Human Understanding By John Locke Book II: Of Ideas, Chapters 12-33

5. Because then means, in propriety of speech, to correspond to the ideas in some other mind.

Therefore these complex ideas of MODES, which they are referred by the mind, and intended to correspond to the ideas in the mind of some other intelligent being, expressed by the names we apply to them, they may be very deficient, wrong, and inadequate; because they agree not to that which the mind designs to be their archetype and pattern: in which respect only any idea of modes can be wrong, imperfect, or inadequate. And on this account our ideas of mixed modes are the most liable to be faulty of any other; but this refers more to proper speaking than knowing right.

6. Ideas of Substances, as referred to real Essences, not adequate.

Thirdly, what IDEAS WE HAVE OF SUBSTANCES, I have above shown. Now, those ideas have in the mind a double reference: 1. Sometimes they are referred to a supposed real essence of each species of things. 2. Sometimes they are only designed to be pictures and representations in the mind of things that do exist, by ideas of those qualities that are discoverable in them. In both which ways these copies of those originals and archetypes are imperfect and inadequate.

First, it is usual for men to make the names of substances stand for things as supposed to have certain real essences, whereby they are of this or that species: and names standing for nothing but the ideas that are in men's minds, they must constantly refer their ideas to such real essences, as to their archetypes. That men (especially such as have been bred up in the learning taught in this part of the world) do suppose certain specific essences of substances, which each individual in its several kinds is made conformable to and partakes of, is so far from needing proof that it will be thought strange if any one should do otherwise. And thus they ordinarily apply the specific names they rank particular substances under, to things as distinguished by such specific real essences. Who is there almost, who would not take it amiss if it should be doubted whether he called himself a man, with any other meaning than as having the real essence of a man? And yet if you demand what those real essences are, it is plain men are ignorant, and know them not. From whence it follows, that the ideas they have in their minds, being referred to real essences, as to archetypes which are unknown, must be so far from being adequate that they cannot be supposed to be any representation of them at all. The complex ideas we have of substances are, as it has been shown, certain collections of simple ideas that have been observed or supposed constantly to exist together. But such a complex idea cannot be the real essence of any substance; for then the properties we discover in that body would depend on that complex idea, and be deducible from it, and their necessary connexion with it be known; as all properties of a triangle depend on, and, as far as they are discoverable, are deducible from the complex idea of three lines including a space. But it is plain that in our complex ideas of substances are not contained such ideas, on which all the other qualities that are to be found in them do depend. The common idea men have of iron is, a body of a certain colour, weight, and hardness; and a property that they look on as belonging to it, is malleableness. But yet this property has no necessary connexion with that complex idea, or any part of it: and there is no more reason to think that malleableness depends on that colour, weight, and hardness, than that colour or that weight depends on its malleableness. And yet, though we know nothing of these real essences, there is nothing more ordinary than that men should attribute the sorts of things to such essences. The particular parcel of matter which makes the ring I have on my finger is forwardly by most men supposed to have a real essence, whereby it is gold; and from whence those qualities flow which I find in it, viz. its peculiar colour, weight, hardness, fusibility, fixedness, and change of colour upon a slight touch of mercury, &c. This essence, from which all these properties flow, when I inquire into it and search after it, I plainly perceive I cannot discover: the furthest I can go is, only to presume that, it being nothing but body, its real essence or internal constitution, on which these qualities depend, can be nothing but the figure, size, and connexion of its solid parts; of neither of which having any distinct perception at all can I have any idea of its essence: which is the cause that it has that particular shining yellowness; a greater weight than anything I know of the same bulk; and a fitness to have its colour changed by the touch of quicksilver. If any one will say, that the real essence and internal constitution, on which these properties depend, is not the figure, size, and arrangement or connexion of its solid parts, but something else, called its particular FORM, I am further from having any idea of its real essence than I was before. For I have an idea of figure, size, and situation of solid parts in general, though I have none of the particular figure, size, or putting together of parts, whereby the qualities above mentioned are produced; which qualities I find in that particular parcel of matter that is on my finger, and not in another parcel of matter, with which I cut the pen I write with. But, when I am told that something besides the figure, size, and posture of the solid parts of that body in its essence, something called SUBSTANTIAL FORM, of that I confess I have no idea at all, but only of the sound form; which is far enough from an idea of its real essence or constitution. The like ignorance as I have of the real essence of this particular substance, I have also of the real essence of all other natural ones: of which essences I confess I have no distinct ideas at all; and, I am apt to suppose, others, when they examine their own knowledge, will find in themselves, in this one point, the same sort of ignorance.

7. Because men know not the real essence of substances.

Now, then, when men apply to this particular parcel of matter on my finger a general name already in use, and denominate it GOLD, do they not ordinarily, or are they not understood to give it that name, as belonging to a particular species of bodies, having a real internal essence; by having of which essence this particular substance comes to be of that species, and to be called by that name? If it be so, as it is plain it is, the name by which things are marked as having that essence must be referred primarily to that essence; and consequently the idea to which that name is given must be referred also to that essence, and be intended to represent it. Which essence, since they who so use the names know not, their ideas of substances must be all inadequate in that respect, as not containing in them that real essence which the mind intends they should.

8. Ideas of Substances, when regarded as Collections of their Qualities, are all inadequate.

Secondly, those who, neglecting that useless supposition of unknown real essences, whereby they are distinguished, endeavour to copy the substances that exist in the world, by putting together the ideas of those sensible qualities which are found co-existing in them, though they come much nearer a likeness of them than those who imagine they know not what real specific essences: yet they arrive not at perfectly adequate ideas of those substances they would thus copy into their minds: nor do those copies exactly and fully contain all that is to be found in their archetypes. Because those qualities and powers of substances, whereof we make their complex ideas, are so many and various, that no man's complex idea contains them all. That our complex ideas of substances do not contain in them ALL the simple ideas that are united in the things themselves is evident, in that men do rarely put into their complex idea of any substance all the simple ideas they do know to exist in it. Because, endeavouring to make the signification of their names as clear and as little cumbersome as they can, they make their specific ideas of the sorts of substance, for the most part, of a few of those simple ideas which are to be found in them: but these having no original precedency, or right to be put in, and make the specific idea, more than others that are left out, it is plain that both these ways our ideas of substances are deficient and inadequate. The simple ideas whereof we make our complex ones of substances are all of them (bating only the figure and bulk of some sorts) powers; which being relations to other substances, we can never be sure that we know ALL the powers that are in any one body, till we have tried what changes it is fitted to give to or receive from other substances in their several ways of application: which being impossible to be tried upon any one body, much less upon all, it is impossible we should have adequate ideas of any substance made up of a collection of all its properties.

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