ge of a particular occurrence, when accompanied
by a memory-belief, may be said to mean the occurrence of which it is an
image. But most actual images do not have this degree of definiteness.
If we call up an image of a dog, we are very likely to have a vague
image, which is not representative of some one special dog, but of dogs
in general. When we call up an image of a friend's face, we are not
likely to reproduce the expression he had on some one particular
occasion, but rather a compromise expression derived from many
occasions. And there is hardly any limit to the vagueness of which
images are capable. In such cases, the meaning of the image, if defined
by relation to the prototype, is vague: there is not one definite
prototype, but a number, none of which is copied exactly.*

* Cf. Semon, Mnemische Empfindungen, chap. xvi, especially
pp. 301-308.

There is, however, another way of approaching the meaning of images,
namely through their causal efficacy. What is called an image "of"
some definite object, say St. Paul's, has some of the effects which the
object would have. This applies especially to the effects that depend
upon association. The emotional effects, also, are often similar:
images may stimulate desire almost as strongly as do the objects they
represent. And conversely desire may cause images*: a hungry man will
have images of food, and so on. In all these ways the causal laws
concerning images are connected with the causal laws concerning the
objects which the images "mean." An image may thus come to fulfil the
function of a general idea. The vague image of a dog, which we spoke of
a moment ago, will have effects which are only connected with dogs in
general, not the more special effects which would be produced by some
dogs but not by others. Berkeley and Hume, in their attack on general
ideas, do not allow for the vagueness of images: they assume that every
image has the definiteness that a physical object would have This is not
the case, and a vague image may well have a meaning which is general.

* This phrase is in need of interpretation, as appears from
the analysis of desire. But the reader can easily supply the
interpretation for himself.

In order to define the "meaning" of an image, we have to take account
both of its resemblance to one or more prototypes, and of its causal
efficacy. If there were such a thing as a pure imagination-image,
without any prototype whate