When Newton first discovered the property of attraction, and settled its laws, he found it served very well to explain several of the most remarkable phenomena in nature; but yet with reference to the general system of things, he could consider attraction but as an effect, whose cause at that time he did not attempt to trace. But when he afterwards began to account for it by a subtle elastic aether, this great man (if in so great a man it be not impious to discover anything like a blemish) seemed to have quitted his usual cautious manner of philosophising: since, perhaps, allowing all that has been advanced on this subject to be sufficiently proved, I think it leaves us with as many difficulties as it found us. That great chain of causes, which linking one to another even to the throne of God himself, can never be unravelled by any industry of ours. When we go but one step beyond the immediate sensible qualities of things, we go out of our depth. All we do after is but a faint struggle, that shows we are in an element which does not belong to us.
THEORY AND PRACTICE.
It is, I own, not uncommon to be wrong in theory, and right in practice; and we are happy that it is so. Men often act right from their feelings, who afterwards reason but ill on them from principle: but as it is impossible to avoid an attempt at such reasoning, and equally impossible to prevent its having some influence on our practice, surely it is worth taking some pains to have it just, and founded on the basis of sure experience.
INDUCTION AND COMPARISON.
We must not attempt to fly, when we can scarcely pretend to creep. In considering any complex matter, we ought to examine every distinct ingredient in the composition, one by one; and reduce everything to the utmost simplicity; since the condition of our nature binds us to a strict law and vary narrow limits. We ought afterwards to re-examine the principles by the effect of the composition, as well as the composition by that of the principles. We ought to compare our subject with things of a similar nature, and even with things of a contrary nature; for discoveries may be, and often are, made by the contrast, which would escape us on the single view. The greater number of the comparisons we make, the more general and the more certain our knowledge is likely to prove, as built upon a more extensive and perfect induction.