An object is not first imagined or thought about and then expected or willed, but in being actively expected it is imagined as future and in being willed it is thought.
The sensory acts are accordingly distinguished by their objects.
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.
You can mark in desire the rising of the tide, as the appetite more and more invades the personality, appealing, as it does, not merely to the sensory side of the self, but to its ideal components as well.
But unfortunately Locke treated ideas of reflection as if they were another class of objects of contemplation beside ideas of sensation.
The perceptive act is a reaction of the mind upon the object of which it is the perception.
What is the meaning of the togetherness of the perceiving mind, in that peculiar modification of perceiving which makes it perceive not a star but a tree, and the tree itself, is a problem for philosophy.
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.