231. This ‘vicious circle’ was nothing of which Locke need have been ashamed, if only he had understood and avowed its necessity. Body is to solidity and to the primary qualities in general simply as a substance to the relations that determine it; and the ‘circle’ in question merely represents the logical impossibility of defining a substance except by relations, and of defining these relations without presupposing a substance. It was only Locke’s confusion of the order of logical correlation with the sequence of feelings in time, that laid him open to the charge of making body and the ideas of primary qualities, and again the latter ideas and those of secondary qualities, at once precede and follow each other. To avoid this confusion by recognising the logical order--the order of intellectual ‘fictions’--as that apart from which the sequence of feelings would be no order of knowable reality at all, would be of course impossible for one who took Locke’s antithesis of thought and fact for granted. The time for that was not yet. A way of escape had first to be sought in a more strict adherence to Locke’s identification of the sequence of feelings with the order of reality. Hence Hume’s attempt, reversing Locke’s derivation of ideas of sense from primary qualities of body, to derive what with Locke had been primary qualities, as compound impressions of sense, from simple impressions and to reduce body itself to a name not for any ‘just and consistent idea,’ but for a ‘propensity to feign,’ the gradual product of custom and imagination. The question by which the value of such derivation and reduction is to be tried is our old one, whether it is not a tacit conversion of the supposed original impressions into qualities of body that alone makes them seem to yield the result required of them. If the Fourth Book of the ‘Treatise on Human Nature,’ with its elimination of the idea of body, had come before the second, would not the plausibility of the account of mathematical ideas contained in the latter have disappeared? And conversely, if these ideas had been reduced to that which upon elimination of the idea of body they properly become, would not that ‘propensity to feign,’ which is to take the place of the excluded idea, be itself unaccountable? With Hume ‘body’ logically disappears. What then?