§ 2. Distinction and Relation of Image and Idea. — An idea can no more exist without an image than perception can exist without sensation. But the image is no more identical with the idea than sensation is identical with perception. The image is only one constituent of the idea; the other and more important constituent is the meaning which the image conveys. If I think about the Duke of Wellington, the image present to my consciousness may be only the shadowy outline of an aquiline nose. But this of course is not my idea of the Duke of Wellington. My idea includes the cumulative result of many complex mental processes, such as the reading of Napier's Peninsula War, etc. If I had been thinking of some one else with an aquiline nose, my mental attitude would have been very different indeed. This example shows that virtually the same mental image may have very different meanings according to context and circumstances. The meaning varies with the train of thought in which the image occurs.

There are some people, especially those who are much occupied with abstract thinking, who are inclined to deny that they have any mental imagery at all. They are almost or quite unable to visualise objects, and their general power of mentally reviving auditory and tactile experiences may also be rudimentary. The images which with them mark the successive steps in a train of ideas are mainly or wholly verbal. What they mentally reinstate in the way of an image is the motor process of articulation, or the sound of spoken words, or both. The words and their meaning are all that are present to consciousness in such cases. Images resembling features or concomitants of the object thought about, are absent. But it is inaccurate to say that such persons think without images; for the verbal image is just as much an image in the psychological sense as a visual picture of the object is.

It should be noted however that the verbal image is capable of conveying a kind of meaning which the visual picture or other revivals imitative of the object itself cannot of themselves convey. All higher modes of conceptual thinking are possible only by means of words. To conceive is to think of the general or universal in contradistinction from the particulars which it embraces and connects. If I think of life, for instance, I think of a general kind of process manifested in an indefinite diversity of special ways. The word life enables me to fix attention on the common form of process in contradistinction to its manifold modes of manifestation. A mental picture imitative of the object could not fulfil the same function if it were not accompanied by the word life. At any rate it could do so only very imperfectly; and certainly a mind which depended merely on such pictures or similar images could never have formed the conception of life in general for the first time. An imitative image may represent some very special and obvious manifestation of life, but not life in general in contradistinction from its particular phenomena.

Conceptual process may be regarded as a higher development of ideational process. As we shall see later on, the transition is a gradual one, and the germs of conception are present even in rudimentary trains of ideas. What concerns us here is that even the highest developments of conception still involve imagery, though the imagery may be and often is, purely verbal. In the present chapter we have to deal with the nature of mental imagery in general as distinguished from perceptual experiences.