128. To a reader to whom Locke’s language has always seemed to be--as indeed it is--simply that of common sense and life, in writing the above we shall seem to be creating a difficulty where none is to be found. Let us turn, then, to one of the less prolix passages, in which the distinction between the two sources of ideas is expressed: ‘External objects furnish the mind with the ideas of sensible qualities, which are all those different perceptions they produce in us; and the mind furnishes the understanding with ideas of its own operations’ (Book II. chap. i. sec. 5). We have seen already that with Locke perception and idea are equivalent terms. It only needs further to be pointed out that no distinction can be maintained between his usage of ‘mind’ and of ‘understanding,’ [1] and that the simple ideas of the mind’s own operations are those of perception and power, which must be given in and with every idea of a sensible quality.’ [2] Avoiding synonyms, then, and recalling the results of our examination of the terms involved in the first clause of the passage before us, we may re-write the whole thus: ‘Creations of the mind, which yet are external to it, produce in it those perceptions of their qualities which they do produce; and the mind produces in itself the perception of these, its own, perceptions.’ [1] As becomes apparent on examination of such passages, as Book II. chap. i. sec. 1, sub. fin.; and Book II. chap. i. sec. 23. [2] See above, paragraphs 11, 12, 16. That which is the source of substantiation cannot be itself a substance.