209. This amounts to a full acceptance of Berkeley’s doctrine of sense; and the question necessarily arises--such being the impression, and all ideas being impressions grown weaker, can there be an idea of relation at all? Is it not open to the same challenge which Hume offers to those who talk of an idea of substance or of spirit? ‘It is from some one impression that every real idea is derived.’ What, then, is the one impression from which the idea of relation is derived? ‘If it be perceived by the eyes, it must be a colour; if by the ears, a sound; if by the palate, a taste; and so of the other senses.’ There remain ‘our passions and emotions;’ but what passion or emotion is a resemblance, or a proportion, or a relation of cause and effect? Only in regard to identity and causation that he sees any difficulty. These he treats as fictions resulting from ‘natural relations’ of ideas: _i.e._ from resemblance and contiguity. 210. Respect for Hume’s thoroughness as a philosopher must be qualified by the observation that he does not attempt to meet this difficulty in its generality, but only as it affects the relations of identity and causation. The truth seems to be that he wrote with Berkeley steadily before his mind; and it was Berkeley’s treatment of these two relations in particular as not sensible but intelligible, and his assertion of a philosophic Theism on the strength of their mere intelligibility, that determined Hume, since it would have been an anachronism any longer to treat them as sensible, to dispose of them altogether. The condition of his doing so with success was that, however unwarrantably, he should treat the other relations as sensible. The language, which seems to express ideas of the two questionable relations, he has to account for as the result of certain impressions of reflection, called ‘propensities to feign,’ which in their turn have to be accounted for as resulting from the _natural_ relations of ideas according to the definition of these quoted above, [1] as ‘the qualities by which one idea habitually introduces another.’ Among these, as we saw, he included not only resemblance and contiguity in time or place, but ‘cause and effect.’ ‘There is no relation,’ he says, ‘which produces a stronger connection in the fancy than this.’ But in this, as in much of the language which gives the first two Parts their plausibility, he is taking advantage of received notions on the part of the reader, which it is the work of the rest of the book to set aside. In any sense, according to him, in which it differs from usual contiguity, the relation of cause and effect is itself reducible to a ‘propensity to feign’ arising from the other natural relations; but when the reader is told of its producing ‘a strong connection in the fancy,’ he is not apt to think of it as itself nothing more than the product of such a connection. For the present, however, we have only to point out that Hume, when he co-ordinates it with the other natural