THOUGHT AND THOUGHT CONTENT
So far we have been considering only sense data and relations as perceived. But perception is not the only way in which we can be conscious of objects. We can imagine or think of things which are not "present to sense." At the present moment, I may look at the blue-covered match box on my desk: that is perception. Then I may close my eyes and still be conscious of the box: that is imagination.
The terms thought of and thought about are commonly used in slightly different applications. When I am conscious of the box chiefly as a detached object, rectangular in shape, dark blue on the ends and light blue on the sides, and with any other features which, if the box were perceived, could be present in a single "act" of perception, I am said to think of, or imagine the box. In that case, the relations of which I am conscious are mainly between different parts of the object itself. If, on the other hand, I am aware of the box as it is related to other objects: as a container for matches; as made from a thin sheet of wood by an ingenious machine; as costing, with the contained matches, one cent; as inflammable; and so on, I am said to think about the box. This difference between thinking of and thinking about will be more fully considered in a later section of this chapter.
Imagination and perception are closely related. In general, it is possible to imagine only what has been perceived previously. The medieval philosophers, from whom "common sense" theories are so largely drawn, held that the dependence is absolute. "Nothing," they said, "can be in thought which has not previously been in perception." Whether this sweeping generalization is or is not justified, we shall not attempt to decide until we have considered the important topic of instinct: but certainly there is some truth in it. The adult who has been blind from birth can-