The pattern in which different items in consciousness occur together or in succession. According to associationism, laws of such association would play the same role in the study of conscious processes as laws of nature do in the study of natural phenomena. The first attempt to isolate the properties in virtue of which ideas follow one another is that of Aristotle, De Memoria et Reminiscentia (part of the shorter natural works, trs. as Of Memory and Reminiscence, ii. 451 b 18–20).

Connections whereby one idea leads to another can be seen as sources of delusion (e.g. in Hutcheson, and to some extent in Locke) or as an essential constructive mechanism of the human mind (e.g. in Hume). Associationism, or the belief that there should be such laws, for instance depending on the similarity of ideas or their contiguity in time or place, is an important element in the philosophy of Hartley and especially Hume. It is appealing to empiricists in substituting natural processes for the apparently less tractable processes involved in complex trains of reasoning, or the use of imagination or analogies. It is later developed by Bain, J. S. Mill, and Condillac, but the rise of behaviourism and more sophisticated views about the relationship between consciousness and underlying processes have largely discredited the goal.