Primarily, meaning consists in "objective reference," in the primary judgments of perception. What is important to the so called "feeling" of familiarity is the implicit judgment, "this has occurred before." But the primary judgments of perception de pend upon sensory experience. What, then, is the sensory basis in this case? If it consists neither in changes in the primary attributes of sensation, nor in a distinct imaginal context, it is plausible to suppose that it lies in the less differentiated background in which the sense-presentation is set. Such background need not be all of presentational nature, but may include subjective components, e.g., the experience of difficulty or ease in the process of per ception. The shocks of surprise and the general "organic rever beration" of sensory experience may also play a part, though whether familiarity is a positive quality over and above the mere absence of the feeling of strangeness is difficult to decide.
Similar considerations apply to the more complex case of a succession of varied presentations. The separate items have po tentially characters in their own right, but each is modified in accordance with what has gone before. The particular sense presentation is part of a larger whole and as such it is apprehended.
Nevertheless changes in the internal nature of a sensory ex perience in virtue of what has gone before follows in accordance with an even wider law—what we may call the principle of the unity of experience. Physical things are thought of as remaining constant in their characters in total independence of environmental change except in response to specific causal laws. The colour or size of a flower does not depend upon its background. Within experience, on the contrary, there is universal relativity. The nature of a sense-presentation depends on what has gone before and upon much that simultaneously occurs. Even apparent ex ceptions to this rule are becoming increasingly difficult to discover as quantitative investigations become more exact and refined.
The Transition from Percepts to Free Ideas.—It is dis tinctively characteristic of Percepts that on the side of sense they involve impressional experience,—sensations proper as con trasted with images. But we are now able to have thoughts and trains of thoughts which are quite independent of present sense impressions. Such thoughts are free ideas and they are possible only inasmuch as on the side of sense, images are substituted for impressions. How then do images first arise? They are, as has already been remarked, a relatively late development. All the
evidence would seem to point to their absence in lower stages of mental life. They emerge only when impressional experience has become sufficiently complex and differentiated. How this takes place we have already partly indicated in treating of Differentia tion, Retention and acquirement of meaning. We have now to take account of another side of the same process which we have so far not expressly considered—Complication. When we see snow we are perceptually aware of it as cold, soft and wet much in the same way as we are aware of it as white and extended. There is a "forefeel" of its coldness, softness and wetness (Ward, Psy chological Principles, p. i86). But this is inexplicable if all that is sensibly experienced in perceiving the snow is the visual im pression. There must also be, and introspective analysis shows that there are, revivals of what is retained from past impression able experiences in which we have not only seen but handled snow. Such revivals are inseparably one with or "tied to" the original impression, and, except that they are derivative not primary, are themselves impressions rather than images, or have a character intermediate between the two. They are not substituted for im pressional experience but only make it more complex. Hence the process through which this comes about is fitly called Complica tion, which corresponds at the perceptual level to Association of Ideas.
When differentiation and complication have reached a certain stage, sensory revival is no longer tied to a present primary im pression. It is capable of being set free as a mental image. Other conditions being fulfilled, this takes place when subjective interest requires it, and is coincident with the endeavour to take measures beforehand to meet situations remote in time and place.
Besides this general principle we may also refer to two special conditions which facilitate the emergence of free ideas. The first is the continued effort to attend to a percept after it has ceased to be present to the senses. There thus arises an image which is peculiarly vivid because it blends with and is reinforced by a fading impression. This is what is called the "primary memory image." The second is disappointed perceptual anticipation. What, owing to complication we preperceive as hot turns out to be cold, what we expect to resist our movements crumbles beneath our touch, the egg we are about to eat is found to be an empty shell. What is thus excluded from impressional experience becomes con trasted with it as an image and perception gives place to an idea.