so that many individual perceptions leave but a single blurred
memory that stands for them all, because it combines their several
associations. Similarly, when various objects have many common
characteristics, the mind is incapable of keeping them apart. It
cannot hold clearly so great a multitude of distinctions and
relations as would be involved in naming and conceiving
separately each grain of sand, or drop of water, each fly or horse or
man that we have ever seen. The mass of our experience has
therefore to be classified, if it is to be available at all. Instead of a
distinct image to represent each of our original impressions, we
have a general resultant -- a composite photograph -- of those
impressions.

This resultant image is the idea of the class. It often has very few,
if any, of the sensible properties of the particulars that underlie it,
often an artificial symbol -- the sound of a word -- is the only
element, present to all the instances, which the generic image
clearly contains. For, of course, the reason why a name can
represent a class of objects is that the name is the most
conspicuous element of identity in the various experiences of
objects in that class. We have seen many horses, but if we are not
lovers of the animal, nor particularly keen observers, very likely
we retain no clear image of all that mass of impressions except the
reverberation of the sound "horse," which really or mentally has
accompanied all those impressions. This sound, therefore, is the
content of our general idea, and to it cling all the associations
which constitute our sense of what the word means. But a person
with a memory predominantly visual would probably add to this
remembered sound a more or less detailed image of the animal;
some particular horse in some particular attitude might possibly be
recalled, but more probably some imaginative construction,
some dream image, would accompany the sound. An image which
reproduced no particular horse exactly, but which was a
spontaneous fiction of the fancy, would serve, by virtue of its felt
relations, the same purpose as the sound itself. Such a spontaneous
image would be, of course, variable. In fact, no image can, strictly
speaking, ever recur. But these percepts, as they are called,
springing up in the mind like flowers from the buried seeds of past
experience, would inherit all the powers of suggestion which are
required by any instrument of classification.

These powers