may be compar’d in that particular; which is another very fertile source of relation.
5. When any two objects possess the same quality in common, the degrees, in which they possess it, form a fifth species of relation. Thus of two objects, which are both heavy, the one may be either of greater, or less weight than with the other. Two colours, that are of the same kind, may yet be of different shades, and in that respect admit of comparison.
6. The relation of contrariety may at first sight be regarded as an exception to the rule, that no relation of any kind can subsist without some degree of resemblance. But let us consider, that no two ideas are in themselves contrary, except those of existence and non-existence, which are plainly resembling, as implying both of them an idea of the object; tho’ the latter excludes the object from all times and places, in which it is supposed not to exist.
7. All other objects, such as fire and water, heat, and cold, are only found to be contrary from experience, and from the contrariety of their causes or effects; which relation of cause and effect is a seventh philosophical relation, as well as a natural one. The resemblance implied in this relation, shall be explain’d afterwards.
It might naturally be expected, that I should join difference to the other relations. But that I consider rather as a negation of relation, than as any thing real or positive. Difference is of two kinds as oppos’d either to identity or resemblance. The first is called a difference of number; the other of kind.
SECTION VI.
Of modes and substances.
