SECT. V.
Of Relations.
The word RELATION is commonly used in two senses considerably different from each other. Either for that quality, by
which two ideas are connected together in the imagination, and the one naturally introduces the other, after the manner
above-explained: or for that particular circumstance, in which, even upon the arbitrary union of two ideas in the fancy, we
may think proper to compare them. In common language the former is always the sense, in which we use the word, relation;
and tis only in philosophy, that we extend it to mean any particular subject of comparison, without a connecting principle.
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: as if distance and relation were incompatible.'
It may perhaps be esteemed an endless task to enumerate all those qualities, which make objects admit of comparison, and
by which the ideas of philosophical relation are produced. But if we diligently consider them, we shall find that without
difficulty they may be compriz'd under seven general heads, which may be considered as the sources of all philosophical
relation.
(1) The first is resemblance: And this is a relation, without which no philosophical relation can exist; since no objects will
admit of comparison, but what have some degree of resemblance. But tho' resemblance be necessary to all philosophical
relation, it does not follow, that it always produces a connexion or association of ideas. When a quality becomes very
general, and is common to a great many individuals, it leads not the mind directly to any one of them; but by presenting at
once too great a choice, does thereby prevent the imagination from fixing on any single object.
(2) Identity may be esteem'd a second species of relation. This relation I here consider as apply'd in its strictest sense to
constant and unchangeable objects; without examining the nature and foundation of personal identity, which shall find its
place afterwards. Of all relations the most universal is that of identity, being common to every being whose existence has any
duration.
(3) After identity the most universal and comprehensive relations are those of Space and Time, which are the sources of an
infinite number of comparisons, such as distant, contiguous, above, below, before, after, etc.
(4) All those objects, which admit of quantity, or number, 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 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 anything real or positive. Difference is of two kinds as oppos'd either to identity or resemblance. The first is
call'd a difference of number; the other of kind.