214, His account of the idea of a substance [1] is simply Locke’s, as Locke’s would become upon elimination of the notion that there is a real ‘something’ in which the collection of ideas subsist, and from which they result. It thus avoids all difficulties about the relation between nominal and real essence. Just as Locke says that in the case of a ‘mixed mode’ the nominal essence _is_ the real, so Hume would say of a substance. The only difference is that while the collection of ideas, called a mixed mode, does not admit of addition without a change of its name, that called a substance does. Upon discovery of the solubility of gold in aqua regia we add that idea to the collection, to which the name ‘gold’ has previously been assigned, without disturbance in the use of the name, because the name already covers not only the ideas of certain qualities, but also the idea of a ‘principle of union’ between them, which will extend to any ideas presented along with them. As this principle of union, however, is not itself any ‘real essence,’ but ‘part of the complex idea,’ the question, so troublesome to Locke, whether a proposition about gold asserts real co-existence or only the inclusion of an idea in a nominal essence, will be superfluous. How the ‘principle of union’ is to be explained, will appear below. [2] [1] p. 324 [Book I, part I., sec. VI.] [2] Paragraph 303, and the following. How can ideas ‘in flux’ be collected? 215. There are names, then, which represent ‘collections of ideas.’ How can we explain such collection if ideas are merely related feelings grown’ fainter? Do we, when we use one of these names significantly, recall, though in a fainter form, a series of feelings that we have experienced in the process of collection? Does the chemist, when he says that gold is soluble in aqua regia, recall the visual and tactual feeling which he experienced when he found it soluble? If so, as that feeling took its character from relation to a multitude of other ‘complex ideas,’ he must on the same principle recall in endless series the sensible occurrences from which each constituent of each constituent of these was derived; and a like process must be gone through when gold is pronounced ductile, malleable, &c. But this would be, according to the figure which Hume himself adopts, to recall a ‘perpetual flux.’ The very term ‘collection of ideas,’ indeed, if this be the meaning of ideas, is an absurdity, for how can a perpetual flux be collected? If we turn for a solution of the difficulty to the chapter where Hume expressly discusses the significance of general names, we shall find that it is not the question we have here put, and which flows directly from his account of ideas, that he is there treating, but an entirely different one, and one that could not be raised till for related feeling had been substituted the thought of an object under relations. Are there general ideas? Berkeley said, ‘yes and no’.