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

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

But though cognition is not an element of mental action, nor even in any real sense of the word an aspect of it, the distinction of cognition and conation has if properly defined a definite value.

Desire then is the invasion of the whole self by the wish, which, as it invades, sets going more and more of the psychical processes; but at the same time, so long as it remains desire, does not succeed in getting possession of the self.

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.

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

The mental act of sensation which issues in reflex movement is so simple as to defy analysis.