Association of Ideas, in Psychology, the connection in the mind between two ideas, so that the one tends to recall the other. Thus the sight of a particular place may recall an event which has happened there; the mention of a particular word in a conversation may recall a previous conversation. The laws which govern the association of ideas are those of contiguity and similarity. Thus, for instance, an action or idea which has occurred simultaneously or in close succession to another, recalls the second when it (the first) is again presented to the mind; and similarly with respect to actions or ideas which have any resemblance to each other. Some psychologists hold that other laws - such as the laws of contrariety, analogy, etc. - exist; but most agree that all are reducible to the two above-mentioned. These laws, virtually stated by Aristotle in his treatise on Memory, have been given a most important place in psychology by Hartley and Hume in the last century, and by James and J. S. Mill and Prof. Bain in this, who are followed to some extent by Herbert Spencer, and are sometimes referred to collectively as the "Associationist School of Psychologists," in the explanation of the phenomena of intellect.