301. Relation in the way of identity is treated by Hume in the third part of the Treatise [1] pretty much as he treats contiguity and distance. He admits that it does not depend on the nature of any ideas so related--in other words, that it is not constituted by feelings as they would be for a merely feeling consciousness--yet he denies that the mind ‘in any observations we may make concerning it’ can go beyond what is immediately present to the senses. Directly afterwards, however, we find that there _is_ a judgment of identity which involves a ‘conclusion beyond the impressions of our senses’--the judgment, namely, that an object of which the perception is interrupted continues individually the same notwithstanding the interruption. Such a judgment, we are told, is a supposition founded only on the connection of cause and effect. How any ‘observation concerning identity’ can be made without it is not there explained, and, pending such explanation, observations concerning identity are freely taken for granted as elements given by sense in the experience from which the judgment of cause and effect is derived. In the second chapter of Part IV., however, where ‘belief in an external world’ first comes to be explicitly discussed by Hume, we find that ‘propensities to feign’ are as necessary to account for the judgment of identity as for that of necessary connection. If that chapter had preceded, instead of following, the theory of cause and effect as given in Part III., the latter would have seemed much less plain sailing than to most readers it has done. It is probably because nothing corresponding to it appears in that later redaction of his theory by which Hume sought popular acceptance, that the true suggestiveness of his speculation was ignored, and the scepticism, which awakened Kant, reduced to the commonplaces of inductive logic. To examine its purport is the next step to be taken in the process of testing the possibility of a ‘natural history’ of knowledge. Its bearing on the doctrine of cause will appear as we proceed. [1] P. 376. [Book I, part III., sec. II.] Identity of objects an unavoidable crux for Hume. His account of it.