A Treatise of Human Nature / Being an Attempt to Introduce the Experimental Method Into Moral Subjects; and Dialogues Concerning Natural Religion

by David Hume

Relation of cause has to be put into sensitive experience in order to be got from it.

70. We thus find that it is only so far as simple ideas are referred to things—only so far as each in turn, to use Locke’s instance, is regarded as an appearance ‘in a substance which was not in it before’—that our sensitive experience, the supposed datum of knowledge, is an experience of the vicissitudes of things; and again, that only as an experience of such vicissitude does it furnish the ‘observation from which we get our ideas of cause and effect.’ But the reference of a sensation to a sensible thing means its reference to a cause. In other words, the invented relation of cause and effect must be found in the primary experience in order that it may be got from it. [1]

[1] Locke’s contradiction of himself in regard to this relation might be exhibited in a still more striking light by putting side by side with his account of it his account of the idea of power. The two are precisely similar, the idea of power being represented as got by a notice of the alteration of simple ideas in things without (Book II. chap. xxi. sec. 1), just as the idea of cause and effect is. Power, too, he expressly says, is a relation. Yet, although the idea of it, both as derived and as of a relation, ought to be complex, he reckons it a simple and original one, and by using it interchangeably with ‘sensible quality’ makes it a primary datum of sense.

Origin of the idea of identity according to Locke.

71. The same holds of that other ‘product of the mind,’ the relation of identity. This ‘idea’ according to Locke, is formed when, ‘considering anything as existing at any determined time and place, we compare it with itself existing at another time.’ ‘In this consists identity,’ he adds, ‘when the ideas it is attributed to, vary not at all from what they were that moment wherein we consider their former existence, and to which we compare the present; for we never finding nor conceiving it possible that two things of the same kind should exist in the same place at the same time, we rightly conclude that whatever exists anywhere, at any time, excludes all of the same kind, and is there itself alone. When, therefore, we demand whether anything be the same or no? it refers always to something that existed such a time in such a place, which it was certain at that instant was the same with itself, and no other; from whence it follows that one thing cannot have two beginnings of existence, nor two things one beginning; it being impossible for two things of the same kind to be or exist in the same instant in the very same place, or one and the same thing in different places. That, therefore, that had one beginning, is the same thing; and that which had a different beginning in time and place from that is not the same, but diverse.’ He goes on to inquire about the principium individuationis, which he decides is ‘existence itself, which determines a being of any sort to a particular time and place, incommunicable to two beings of the same kind … for being at that instant what it is and nothing else, it is the same, and so must continue as long as its existence is continued; for so long it will be the same, and no other.’ (Book II. chap, xxvii. secs. 1-3).

Relation of identity not to be distinguished from idea of it.

72. It is essential to bear in mind with regard to identity, as with regard to cause and effect, that no distinction according to Locke can legitimately be made between the relation and the idea of the relation. As to substance, it is true, he was driven in his controversy with Stillingfleet to distinguish between ‘the being and the idea thereof,’ but in dealing with relation he does not attempt any such violence to his proper system. Between the ‘idea’ as such and ‘being’ as such, his ‘new way of ideas,’ as Stillingfleet plaintively called it, left no fair room for distinction. In this indeed lay its permanent value for speculative thought. The distinction by which alone it could consistently seek to replace the old one, so as to meet the exigencies of language and knowledge, was that between simple ideas, as given and necessarily real, and the reproductions or combinations in which the mind may alter them. But since every relation implies a putting together of ideas, and is thus always, as Locke avows, a complex idea or the work of the mind, a distinction between its being and the idea thereof, in that sense of the distinction in which alone it can ever be consistently admitted by Locke, was clearly inadmissible. Thus in the passages before us the relation of identity is not explicitly treated as an original ‘being’ or ‘existence,’ It is an idea formed by the mind upon a certain ‘consideration of things’ being or existent. But on looking closely at Locke’s account, we find that it is only so far as it already belongs to, nay constitutes, the things, that it is formed upon consideration of them.

This ‘invented’ relation forms the ‘very being of things’.

73. When it is said that the idea of identity, or of any other relation, is formed upon consideration of things as existing in a certain way, this is naturally understood to mean—indeed, otherwise it is unmeaning—that the things are first known as existing, and that afterwards the idea of the relation in question is formed. But according to Locke, as we have seen, [1] the first and simplest act of knowledge possible is the perception of identity between ideas. Either then the ‘things,’ upon consideration of which the idea of identity is formed, are not known at all, or the knowledge of them involves the very idea afterwards formed on consideration of them. Locke, having at whatever cost of self-contradiction to make his theory fit the exigencies of language, virtually adopts the latter alternative, though with an ambiguity of expression which makes a definite meaning difficult to elicit. We have, however, the positive statement to begin with, that the comparison in which the relation originates, is of a thing with itself as existing at another time. Again, the ‘ideas’ (used interchangeably with ‘things’), to which identity is attributed, ‘vary not at all from what they were at that moment wherein we consider their former existence.’ It is here clearly implied that ‘things’ or ‘ideas’ exist, i.e. are given to us in the spontaneous consciousness which we do not make, as each one and the same throughout a multiplicity of times. This, again, means that the relation of identity or sameness, i.e. unity of thing under multiplicity of appearance, belongs to or consists in the ‘very being’ of those given objects of consciousness, which are in Locke’s sense the real, and upon which according to him all relation is superinduced by an after-act of thought. So long as each such object ‘continues to exist,’ so long its ‘sameness with itself must continue,’ and this sameness is the complex idea, the relation, of identity. Just as before, following Locke’s lead, we found the simple idea, as the element of knowledge, become complex—a perceived identity of ideas; so now mere existence, the ‘very being of things’ (which with Locke is only another name for the simple idea), resolves itself into a relation, which it requires ‘consideration by the mind’ to constitute.

[1] See above, paragraph 25.