In the perception of a tree we can distinguish the act of experiencing, or perceiving, from the thing experienced, or perceived.
Psychology is the science of the act of experiencing, and deals with the whole system of such acts as they make up mental life.
When we come to images or memories or thoughts, speculation, while always closely related to practice, is more explicit, and it is in fact not immediately obvious that such processes can be described in any sense as practical.
It is more difficult to designate this form of conation on its practical side by a satisfactory name.
It is convenient to distinguish the two kinds of experience which have thus been described, the experienc-ing and the experienc-ed, by technical words.