Psychology is the science of the act of experiencing, and deals with the whole system of such acts as they make up mental life.

Both expectations and memories are more than mere images founded on previous experience.

In the perception of a tree we can distinguish the act of experiencing, or perceiving, from the thing experienced, or perceived.

Thus the same object may supply a practical perception to one person and a speculative one to another, or the same person may perceive it partly practically and partly speculatively.

Such being the nature of mental life, the business of psychology is primarily to describe in detail the various forms which attention or conation assumes upon the different levels of that life.

The perceptive act is a reaction of the mind upon the object of which it is the perception.

It may be added, to prevent misunderstanding, that when I speak of contemplated objects in this last phrase as objects of contemplation, the act of contemplation itself is of course an enjoyment.