moment.... There is properly no simplicity in the mind at one time nor identity at different’. [1] [1] pp. 533 and 534 [Book I., part IV., sec. VI.] ... in regard to relations. His account of these. 206. His position in regard to ideas of relation cannot be so summarily exhibited. It is from its ambiguity, indeed, that his system derives at once its plausibility and its weakness. In the first place, it is necessary, according to him, to distinguish between ‘natural’ and ‘philosophical relation.’ The latter is one of which the idea is acquired by the comparison of objects, as distinct from natural relation or ‘the quality by which two ideas are connected together in the imagination, and the one naturally’ (_i.e._ according to the principle of association) ‘introduces the other’. [1] Of philosophical relation--or, according to another form of expression, of ‘qualities by which the ideas of philosophical relation are produced’--seven kinds are enumerated; viz. ‘resemblance, identity, relations of time and place, proportion in quantity and number, degrees in quality, contrariety, and causation’. [2] Some of these do, some do not, _apparently_ correspond to the qualities by which the mind is _naturally_ ‘conveyed from one idea to another;’ or which, in other words, constitute the ‘gentle force’ that determines the order in which the imagination habitually puts together ideas. Freedom in the conjunction of ideas, indeed, is implied in the term ‘imagination,’ which is only thus differenced from ‘memory;’ but, as a matter of fact, it commonly only connects ideas which are related to each other in the way either of resemblance, or of contiguity in time and place, or of cause and effect. Other relations of the philosophical sort are the opposite of _natural_. Thus, ‘distance will be allowed by philosophers to be a true relation, because we acquire an idea of it by the comparing of objects; but in a common way we say, “that nothing can be more distant than such or such things from each other; nothing can have less relation”’ (ibid.). [1] p. 322 [Book I, part I., sec. V.] [2] ibid., and p. 372 [Book I., part III., sec. I.] It corresponds to Locke’s account of the sorts of agreement between ideas.