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.

Curiosity begins as an act of tearing to pieces or analysis.

It is more difficult to designate this form of conation on its practical side by a satisfactory name.

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

The thing of which the act of perception is the perception is experienced as something not mental.

An expectation is a future object, recognised as belonging to me.

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.