=Interpreting Ideas Already Known.=--It is to be noticed at the outset that all ideas selected to aid in the solution of the lesson problem have their origin in certain past experiences which have a bearing on the subject in hand. When presented with a strange object (guava), a person fixes his attention upon it, and thereupon is able, through his former sensation experiences, to interpret it as an unknown thing. He then begins to select, out of his experiences of former objects, ideas that bear upon the thing before him. By focusing thereon certain ideas with which he is perfectly familiar, as rind, flesh, seed, etc., he interprets the strange thing as a kind of fruit. In the same way, when the student is first presented in school with an example of the infinitive, he brings to bear upon the vague presentation various ideas already contained within his experience through his previous study of the noun and the verb. To the extent also to which he possesses and is able to recall these necessary old ideas, will he be able to adjust himself to the new and unfamiliar presented example (infinitive). It is evident, therefore, that a new presentation can have a meaning for us only as it is related to something in our past experience. =Further Examples.=--The mind invariably tries to interpret new presentations in terms of old ideas. A newspaper account of a railway wreck will be intelligible to us only through the revival and reconstruction of those past experiences that are similar to the elements described in the account. The grief, disappointment, or excitement of another will be appreciated only as we have experienced similar feelings in the past. New ideas are interpreted by means of related old ideas; new feelings and acts are dependent upon and made possible by related old feelings and acts. Moreover, the meaning assigned to common objects varies with different persons and even with the same person under different circumstances. A forest would be regarded by the savage as a place to hide from the attacks of his enemies; by the hunter as a place to secure game; by the woodcutter as affording firewood; by the lumberman as yielding logs for lumber; by the naturalist as offering opportunity for observing insects and animals; by the artist as a place presenting beautiful combinations of colours. This ability of the mind to retain and use its former knowledge in meeting and interpreting new experiences is known in psychology as _apperception_. A more detailed study of apperception as a mental process will be made in Chapter XXVI. THE SELECTING PROCESS