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 KAXT HAS yOT ANSWERED HUME. 535
 * >.^y with any otlier simple ideas, whose co-existence with them we

would inform ourselves about. Because the connexion between most simple ideas is unknown (ibidem, 10). (12) There is no discoverable con- nexion between any secondary quality and those primary qualities that it depends on (ib., 12). (13) We can by no means conceive how any size, figure, or motion of any particles can possibly produce in us the idea of any colour, taste, or sound whatsoever ; there is no conceivable connexion betwixt the one and the other (ib., 13). (14) In vain, therefore, shall we endeavour to discover by our ideas (the only true way of certain and uni- 1 knowledge), what other ideas are to be found constantly joined with that of our complex idea of any substance ; since we neither know the real constitution of the minute parts on which their qualities do depend ; nor, did we know them, could we discover any necessary connexion between them. Our knowledge in all these inquiries reaches very little farther than our experience. We cannot know certainly any two ideas to co-exist any farther than experience by our senses informs ns (ib., 14). (15) A the powers of sul "stances to change the sensible qualities of other bodies, I doubt as to these whether our knowledge reaches much farther than our experience (ib., 16). (16) We are ignorant of the several powers, eHk and ways of operation whereby the effects which we daily see are produced (ib., 24). (17) We cannot tell what effects they (bodies) will produce ; nor when we see those effects can we so much as guess, much less know, their manner of production (ib., 26). (18) Though causes work steadily, and effects constantly flow from them, yet, their connexions and dependencies being not discoverable in our ideas, we can have but an experimental knowledge of them. Several effects come every day within the notice of our senses, of which we have so far sensitive knowledge ; but the ca manner and certainty of production we must be content to be ignorant of. In these we can go no farther than particular experience informs us of matter of fact, and by analogy to guess what effects the like bodies are, npon other trials, like to produce (ib., 29). (19) Some of our ideas have a natural correspondence and connexion with one another [as the mathema- tical] ; besides this, there is another connexion of ideas wholly owing to chance or custom ; ideas that are in themselves not at all akin, come to be so united in some men's minds that it is very hard to separate them, they always keep in company, and the one no sooner at any time comes into the understanding, but its associate appears with it (ii, 33, 5). (20) We cannot with certainty affirm that all men sleep by intervals, that no man can be nourished by wood or stones, that all men will be poisoned by hemlock. We must, in these and the like, appeal to trial in particular subjects, which can reach but a little way (iv., 6, 15). (21) God has annexed effects to motion which we can no way conceive motion able to produce (iv., 3, 6). (22) God has set some things in broad daylight, as he _iven us some certain knowledge ; but in the greatest part of our con- cernment he has afforded us only the twilight of probability. The faculty which God has given us to supply the want of clear and certain knowledge in cases where that cannot be had is judgment. Custom, habits, come at last to produce actions in us which often escape our observations ; and, therefore, it is not so strange that our mind should often change the idea of its sensation into that of its judgment, and make one serve only to excite the other without our taking notice of it : we take that for the perception of our sensation which is an idea formed by our judgment (ii., 9, 10 and 9). (23) Not imagining bow these simple ideas can subsist by themselves, we accustom ourselves to suppose some substratum wherein they do subsist, from which they result ; which therefore we call substance. We call it by one name of substance, from the custom of supposing a sub-