This point will have to be touched later on.

Here it is enough to say that, whatever our philosophy of perception may be, we must accept the psychological fact that the concrete mental state in the act of perception is built up out of elements, the history of which can be traced by the methods of mental science.
_Psychology of Perception._ Confining ourselves for the present to the mental, as distinguished from the physical, side of the operation, we soon find that perception is not so simple a matter as it might at first seem to be.

When a man on a hot day looks at a running stream and "sees" the delicious coolness, it is not difficult to show that he is really performing an act of mental synthesis, or imaginative construction.

To the sense-impression[5] which his eye now gives him, he adds something which past experience has bequeathed to his mind.

In perception, the material of sensation is acted on by the mind, which embodies in its present attitude all the results of its past growth.