It is owing to this fact, therefore, that objects which resemble each other, or which are very much contrasted in their qualities, are very commonly united in our conceptions. If, for example, we see the countenance of a stranger, some feature will be recognized as familiar. Desire will be awakened to know where and in what other countenance we have seen such a feature or such an expression. This particular feature will thus become abstracted and vivid, and will soon recall that other combination of features for which we are seeking, and of which this has formed a part in our past experience. Thus two objects will be brought before the mind at once, the person who is the stranger, and a conception of another person whom this stranger resembles. All our ideas of contrast are relative. One thing can not be conceived of as very high or very low, as very large or very small, without a previous comparison with some object to determine this relation. Our ideas of poverty and riches, or of happiness and misery, are also _relative_. A person is always considered poor or rich, happy or miserable, by comparing his lot with that of others by whom he is surrounded. As, therefore, all ideas of resemblance or of contrast are gained by comparing two objects together, our conceptions often unite objects that _resemble_ each other or that are _contrasted_ with each other. CHAPTER XIII. IMAGINATION. All operations of mind which are not produced by material things acting upon the senses consist of a continual succession of conceptions. Some of these conceptions are exact pictures of past perceptions, and are attended by the consciousness that such things have existed before, and such are called ideas of memory. Others are conceptions which, by the process of association, are continually recurring, and arranging themselves in new combinations, according to certain laws or principles of association. Imagination has been defined as "that power which the mind possesses of arranging conceptions in new combinations," and it can readily be seen that this includes all the ordinary successions of thought except those of perception and memory. The term imagination has been used in rather a vague manner by writers on the subject. Sometimes it is used to signify all that succession of conceptions which recur according to the laws of association, and sometimes it is used in a more restricted sense. The more limited meaning is the one to which the term is most commonly applied, and it seems to be the one which precision and accuracy in the use of terms demand, and therefore it will now be pointed out.