The third law of association is, that objects which have recently been associated in experience are, on this account, more likely to recall each other than to recall those which were connected with them at a more remote period of time. The passage of time, as a general fact, seems to weaken the vividness of our conceptions, and to destroy the probability of their associate recurrence. Thus a line of poetry may be repeated, and the listener may be able, the moment after, to recall each word, but the next day the whole may be lost.

The fourth law of association is, that the recurrence of associated objects depends, in a great measure, upon the number of objects with which it may have been connected in past experience. If it has existed in combination with only one object, that object will return associated with it; but in proportion as the number of its associates increases, the power of determining which will be its next companion diminishes. As an example of this fact may be mentioned the first hearing of a beautiful air by some particular person. The next time it is heard, the idea of this performer will be associated with the sounds; but after it has been sung by a great variety of persons, other circumstances would determine what conceptions this air would recall. It is very probable, in this case, that its notes would recall from among the associated scenes the friend most beloved, or some interesting circumstance that awakened emotion at the time the air was performed.

The principal circumstances which operate in recalling associated ideas have now been pointed out. The next inquiry is, What are those objects and events which ordinarily are most frequently united in our perceptions, and therefore are most likely to return together in our conceptions?

The most common connection of our ideas of perception are made by contiguity in place. Objects are continually passing before the eye, and they are not in single distinct objects, but in connected groups. Of course, when we perceive any object, we must necessarily observe its several relations to the things by which it is surrounded. If it is a building which meets the eye, it is impossible to observe it without at the same time perceiving the trees around it, the sky above it, and any other objects which are parts of the picture of which this is the prominent object. Of course, objects that are united in one complex picture before the eye when we gain our knowledge of them by perception, will ordinarily return together in our conceptions.

Our ideas, also, are very much connected by contiguity as it respects time. When any two events occur at the same moment of time, or in such near connection that the conception of one remains until the other occurs, they ordinarily will recur together in our after conceptions of them. As an example of this may be mentioned the associations of a family who have been accustomed to close each Sabbath with music. As the still hour of this sacred evening drew on, wherever any wanderer might roam, it is probable that the notes of praise, so often connected with this season, would perpetually steal over the mind, bringing many another image of friends, and kindred, and home.

The mind of man is so constituted that no change can take place in any material object without awakening the idea of some cause. An effect is defined as "some change of state or mode of existence in matter or mind." A cause is defined as "that without which no change would take place in matter or mind, and with which it will take place." As the ideas of cause and effect are so constantly conjoined in all our acts of perception, these ideas will return together in our conceptions. Thus, if we see an instrument which has been the cause of pain, the idea of this effect will be recalled by a conception of the cause; or if the mind is dwelling on the memory of some beautiful painting or poetry, the author of these works will probably recur to the mind in connection with these conceptions.

We sometimes meet with persons of such peculiar habits and dispositions, that, whenever they are encountered, the feelings are wounded or the temper crossed by their ill-timed or ill-natured remarks. The conceptions of such persons will ordinarily be attended by the memory of some pains of which they have been the cause, and the mind will involuntarily shrink from contact with them, as from the points and thorns of a bramble-bush. Those events, therefore, or those objects which have the relation of cause and effect existing between them, will ordinarily be united as objects of conception.

The mind of man is continually noticing the relations which exist between the different objects of its conceptions. As no idea of relation can be gained without comparing two or more things together, those objects which are most frequently compared will naturally be most frequently associated together in our conceptions. It has been shown that language is founded on that principle of the mind which enables us to notice certain qualities in things abstracted from other qualities, and to apply names to objects according as we find certain qualities united in them. Of course, in the use of language, the mind is continually led to notice the particulars in which objects resemble each other, and also the particulars in which they differ; consequently the mind, in learning and in applying names, is continually comparing objects, both to discover the particulars in which they are alike and those in which they differ, so that two objects are thus brought together before the mind.

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.