8. Our ideas of relations often clearer than of the subjects related. Secondly, This further may be considered concerning relation, that though it be not contained in the real existence of things, but something extraneous and superinduced, yet the ideas which relative words stand for are often clearer and more distinct than of those substances to which they do belong. The notion we have of a father or brother is a great deal clearer and more distinct than that we have of a man; or, if you will, paternity is a thing whereof it is easier to have a clear idea, than of humanity; and I can much easier conceive what a friend is, than what God; because the knowledge of one action, or one simple idea, is oftentimes sufficient to give me the notion of a relation; but to the knowing of any substantial being, an accurate collection of sundry ideas is necessary. A man, if he compares two things together, can hardly be supposed not to know what it is wherein he compares them: so that when he compares any things together, he cannot but have a very clear idea of that relation. The ideas, then, of relations, are capable at least of being more perfect and distinct in our minds than those of substances.
Because it is commonly hard to know all the simple ideas which are really in any substance, but for the most part easy enough to know the simple ideas that make up any relation I think on, or have a name for:
v.g. comparing two men in reference to one common parent, it is very easy to frame the ideas of brothers, without having yet the perfect idea of a man. For significant relative words, as well as others, standing only for ideas; and those being all either simple, or made up of simple ones, it suffices for the knowing the precise idea the relative term stands for, to have a clear conception of that which is the foundation of the relation; which may be done without having a perfect and clear idea of the thing it is attributed to. Thus, having the notion that one laid the egg out of which the other was hatched, I have a clear idea of the relation of dam and chick between the two cassiowaries in St. James's Park; though perhaps Ihave but a very obscure and imperfect idea of those birds themselves.
9. Relations all terminate in simple ideas. Thirdly, Though there be a great number of considerations wherein things may be compared one with another, and so a multitude of relations, yet they all terminate in, and are concerned about those simple ideas, either of sensation or reflection, which I think to be the whole materials of all our knowledge. To clear this, I shall show it in the most considerable relations that we have any notion of; and in some that seem to be the most remote from sense or reflection: which yet will appear to have their ideas from thence, and leave it past doubt that the notions we have of them are but certain simple ideas, and so originally derived from sense or reflection.
10. Terms leading the mind beyond the subject denominated, are relative. Fourthly, That relation being the considering of one thing with another which is extrinsical to it, it is evident that all words that necessarily lead the mind to any other ideas than are supposed really to exist in that thing to which the words are applied are relative words: v.g. a man, black, merry, thoughtful, thirsty, angry, extended; these and the like are all absolute, because they neither signify nor intimate anything but what does or is supposed really to exist in the man thus denominated; but father, brother, king, husband, blacker, merrier, &c., are words which, together with the thing they denominate, imply also something else separate and exterior to the existence of that thing.
11. All relatives made up of simple ideas. Having laid down these premises concerning relation in general, I shall now proceed to show, in some instances, how all the ideas we have of relation are made up, as the others are, only of simple ideas; and that they all, how refined or remote from sense soever they seem, terminate at last in simple ideas. I shall begin with the most comprehensive relation, wherein all things that do, or can exist, are concerned, and that is the relation of cause and effect: the idea whereof, how derived from the two fountains of all our knowledge, sensation and reflection, Ishall in the next place consider.
Chapter XXVI
Of Cause and Effect, and other Relations 1. Whence the ideas of cause and effect got. In the notice that our senses take of the constant vicissitude of things, we cannot but observe that several particular, both qualities and substances, begin to exist; and that they receive this their existence from the due application and operation of some other being. From this observation we get our ideas of cause and effect. That which produces any simple or complex idea we denote by the general name, cause, and that which is produced, effect. Thus, finding that in that substance which we call wax, fluidity, which is a simple idea that was not in it before, is constantly produced by the application of a certain degree of heat we call the simple idea of heat, in relation to fluidity in wax, the cause of it, and fluidity the effect.
So also, finding that the substance, wood, which is a certain collection of simple ideas so called, by the application of fire, is turned into another substance, called ashes; i.e., another complex idea, consisting of a collection of simple ideas, quite different from that complex idea which we call wood; we consider fire, in relation to ashes, as cause, and the ashes, as effect. So that whatever is considered by us to conduce or operate to the producing any particular simple idea, or collection of simple ideas, whether substance or mode, which did not before exist, hath thereby in our minds the relation of a cause, and so is denominated by us.