exactly represent." Complex ideas, on the other hand, need not resemble impressions. We can
imagine a winged horse without having ever seen one, but the constituents of this complex idea
are all derived from impressions. The proof that impressions come first is derived from
experience; for example, a man born blind has no ideas of colours. Among ideas, those that retain
a considerable degree of the vivacity of the original impressions belong to memory, the others to
imagination.
There is a section (Book I, Part I, Sec. VII) "Of Abstract Ideas," which opens with a paragraph of
emphatic agreement with Berkeley's doctrine that "all general ideas are nothing but particular
ones, annexed to a certain term, which gives them a more extensive significance, and makes them
recall upon occasion other individuals, which are similar to them." He contends that, when we
have an idea of a man, it has all the particularity that the impression of a man has. "The mind
cannot form any notion of quantity or quality without forming a precise notion of degrees of
each.""Abstract ideas are in themselves individual, however they may become general in their
representation." This theory, which is a modern form of nominalism, has two defects, one logical,
the other psychological. To begin with the logical objection: "When we have found a resemblance
among several objects," Hume says, "we apply the same name to all of them." Every nominalist
would agree. But in fact a common name, such as "cat," is just as unreal as the universal CAT is.
The nominalist solution of the problem of universals thus fails through being insufficiently drastic
in the application of its own principles; it mistakenly applies these principles only to "things," and
not also to words.
The psychological objection is more serious, at least in connection with Hume. The whole theory
of ideas as copies of impressions, as he sets it forth, suffers from ignoring vagueness. When, for
example, I have seen a flower of a certain colour, and I afterwards call up an image of it, the
image is lacking in precision, in this sense, that there are several closely similar shades of colour
of which it might be an image, or "idea," in Hume's terminology. It is not true that "the mind
cannot form any notion of quantity or quality without forming a precise notion of degrees of
each." Suppose you have seen a man whose height is six feet one inch. You retain an image of
him, but it probably would fit a man half an inch taller or shorter. Vagueness