It is a fact familiar in the experience of everybody that the strength of the emotional tone of an object is a function of the clearness of the image which we form of it on recall. We can preserve the feeling tone of a past event or an absent object only if we can keep a vivid image of it; as our image of it becomes vague, our interest in it dissipates. Everywhere in our experience the image mediates between feeling and idea. So in art. Images have no more an independent and self-sufficient status in art than sensations have; like the latter they are a means for the expression of feeling. In the painting of sunlight, for example, the images of warmth carry joyousness and a sense of ease; in the statue, the tactile images convey the emotional response to the represented object. In literature the expressiveness of images is perhaps even more impressive. Consider how longing is aroused by the tactile, gustatory, and thermal images in the oft-quoted lines of Keats:-- O, for a draught of vintage! that hath been Cool'd a long age in the deep-delved earth. Examples might be multiplied indefinitely. In literature alone of the arts, images from all departments of sense can be aroused. Visual images play a greater role there than in painting and sculpture, for the reason that, in the latter, visual sensations take their place--we do not image what we can see. In sculpture, the greater part of the imagery is of touch and motion--in the imagination, we feel the surfaces and move with the represented motions; the whiteness or blackness of the materials prevents the arousal of the image of the color of the body. In painting, besides the temperature images already mentioned, there are touch images--in still-life, for example, when silks and furs are represented; images of odors, in flower pieces; of motion, in pictures which depict motion, as in the racing horses of Degas; of taste, in pictures of wine and fruit. Of course the kind and amount of imagery depend upon the imaginal type to which the spectator belongs and the wealth of the imaginal furnishing of his mind. In any art, moreover, the chief and requisite thing is expression through the sense medium, which should never be obscured by expression through associated images. It is not the primary business of a flower painter to arouse images of perfume, but to compose colors and lines; nor the function of the musician to arouse the visual images which accompany the musical experience of many people, but to compose sounds. In sculpture, on the other hand, images of touch and movement play an almost necessary part, for they are constituent elements in the representation of form and motion; yet it is not indispensable to the appreciation of sculpture that images of the sweet odor of the human body be awakened. The image is seldom the basis of aesthetic appreciation; it is more often its completion. But we shall go into these matters more in detail in our special chapters.