Association of ideas, or mental association, is a process by which representations arise in consciousness, and also for a principle put forward by an important historical school of thinkers to account generally for the succession of mental phenomena. The term is now used mostly in the history of philosophy and of psychology. One idea was thought to follow another in consciousness if it were associated by some principle. The three commonly asserted principles of association were similarity, contiguity, and contrast, while numerous others had been added by the nineteenth century. By the end of the nineteenth century, the significant impact of physiological psychology lead to much of the older associationist theories being rejected.
Everyday observation of the association of one idea or memory with another gives a face validity to the notion. In addition, the notion of association between ideas and behavior gave some early impetus to behaviorist thinking. The core ideas of associationist thinking recur in some recent thought on cognition, especially consciousness.
Early theory The associationist theory is anticipated in Plato's Phaedo, as part of the doctrine of anamnesis. The idea of Simmias is recalled by the picture of Simmias (similarity) and that of a friend by the sight of the lyre on which he played (contiguity). But Aristotle is credited with originating associationist thinking based on this passage:
Both Thomas Hobbes and John Locke are accredited for the initial study of theory of association. The basis of Hobbes's theory of association is that motion is what rules and attributes to mental activity. Hobbes tells us that the associations which already exist in our minds are what rule our flow of imaginations: "But as we have no imagination, whereof we have not formerly had sense, in whole, or in part; so we have no transition from one imagination to another, whereof we never had the like before in our senses.” Much of these rules, Hobbes says, do not really apply in our dreams. The passage is obscure, but it indicates the principles known as contiguity, similarity, and contrast. Similar principles are stated by Zeno the Stoic, by Epicurus (see Diogenes Laertius vii. § 52, x. § 32), and by St Augustine of Hippo (Confessions, x. c. 19). Aristotle's doctrine was expanded and illustrated during throughout the Middle Ages, and in some cases even into the 17th century. William Hamilton listed philosophical authorities who gave prominence to the general fact of mental association - the Spanish philosopher Joannes Lodovicus Vives (1492–1540) especially being exhaustive in his account of memory.
In Thomas Hobbes's psychology much importance is assigned to what he called, variously, the succession, sequence, series, consequence, coherence, train of imaginations or thoughts in mental discourse. But not before David Hume is there an express question as to what are the distinct principles of association. John Locke had, meanwhile, introduced the phrase "association of ideas" as the title of a supplementary chapter incorporated with the fourth edition of his Essay, though with little or no suggestion of its general psychological import. Hume reduced the principles of association to three: similarity, contiguity in time and place, and cause and/or effect. Dugald Stewart suggested resemblance, contrariety, and vicinity in time and place, though he added, as another obvious principle, accidental coincidence in the sounds of words, and further noted three other cases of relation: cause and effect, means and end, and premise and conclusion, as connecting trains of thought under circumstances of special attention. Thomas Reid, made light of association, remarking that it seems to require only the power of habit to explain the spontaneous recurrence of trains of thinking, which become familiar by frequent repetition (Intellectual Powers, p. 387).
Hamilton's own theory of mental reproduction, suggestion, or association is a development of his ideas in Lectures on Metaphysics (vol. ii. p. 223, seq.), which reduced the principles of association to simultaneity and affinity, and these further to one supreme principle of redintegration or totality. In the final scheme he sets out four general laws of mental succession: (1) Associability or possible co-suggestion (all thoughts of the same mental subject are associable or capable of suggesting each other); (2) Repetition or direct remembrance (thoughts identical in a modification, but differing in time, tend to suggest each other); (3) Redintegration, indirect remembrance or reminiscence (thoughts once identical in time, but different as mental modes, are suggestive of each other in the order they originally held); (4) Preference (thoughts are suggested not merely by the general subjective relation subsisting between them, they are also suggested in proportion to the amount of interest they hold to the individual mind).
These special laws logically follow from the general laws above: A - Primary - Modes of the Laws of Repetition and Redintegration: (1) Law of Similars (Analogy, Affinity); (2) Law of Contrast; and (3) Law of Coadjacency (Cause and Effect, etc.). B - Secondary - Modes of the Law of Preference, under the Law of Possibility: (1) Laws of Immediacy and Homogeneity; and (2) Law of Facility.
The Associationist School The Associationist School includes the English psychologists who aimed at explaining all mental acquisitions and the more complex mental processes generally under laws under the associations which their predecessors applied only to simple reproduction. Hamilton, though professing to deal with reproduction only, formulates a number of still more general laws of mental succession: Law of Succession, Law of Variation, Law of Dependence, Law of Relativity or Integration (involving Law of Conditioned), and, finally, Law of Intrinsic or Objective Relativity. These he posits as the highest to which human consciousness is subject, but it is in a sense quite different that the psychologists of the Associationist School intend their appropriation of the principle or principles commonly signalized. In this regard, as far as can be judged from imperfect records, they were anticipated to some extent by the experientialists of ancient times, both Stoic and Epicurean (cf. Diogenes Laertius, as above).
In the period that led to modern philosophy, Hobbes was the first thinker of permanent note to whom this doctrine may be traced. Although he took a narrow view of the phenomena of mental succession, he (after dealing with trains of imagination or "mental discourse") sought in the higher departments of intellect to explain reasoning as a discourse in words, dependent upon an arbitrary system of marks, each associated with or standing for a variety of imaginations. Except for a general assertion that reasoning is a reckoning (otherwise, a compounding and resolving), he had no other account of knowledge to give. The whole emotional side of mind ("the passions") he similarly resolved into an expectation of consequences based on past experience of pleasures and pains of sense. Thus, though he made no serious attempt to justify his analysis in detail, he is undoubtedly to be classed with the associationists of the next century. They, however, were wont to trace their psychological theory no further back than to Locke's Essay. Bishop Berkeley was driven to posit expressly a principle of suggestion or association in these terms: "That one idea may suggest another to the mind, it will suffice that they have been observed to go together, without any demonstration of the necessity of their coexistence, or so much as knowing what it is that makes them so to coexist." (New Theory of Vision, § 25) and, to support the obvious application of the principle to the case of the sensations of sight and touch before him, he constantly urged that association of sound and sense of language which the later school has always put in the foreground, whether as illustrating the principle in general or in explanation of the supreme importance of language for knowledge. It was natural, then, that Hume, coming after Berkeley and assuming Berkeley's results (though he reverted to the larger inquiry of Locke), should be more explicit in his reference to association. But Hume was original also, when he spoke of it as a "kind of attraction which in the mental world will be found to have as extraordinary effects as in the natural, and to show itself in as many and as various forms." (Human Nature, i. 1, § 4)
Other inquirers about the same time conceived of association with this breadth of view, and set themselves to track, as psychologists, its effects in detail.
David Hartley David Hartley is the thinker most precisely identified with the Associationist School. In his Observations on Man, published in 1749 (11 years after Hume's A Treatise of Human Nature and one year after the better known An Enquiry Concerning Human Understanding), opened the path for all the investigations of like nature that have been so characteristic of English psychology. A physician by profession, he sought to combine with an elaborate theory of mental association a minutely detailed hypothesis as to the corresponding action of the nervous system, based upon the suggestion of a vibratory motion within the nerves thrown out by Isaac Newton in the last paragraph of the Principia. So far, however, from promoting the acceptance of the psychological theory, this physical hypothesis proved to have rather the opposite effect, and it began to be dropped by Hartley's followers (as Joseph Priestley, in his abridged edition of the Observations, 1775) before it was seriously impugned from without. When it is studied in the original, and not taken upon the report of hostile critics, who would not, or could not understand it, no little importance must still be accorded to the first attempt, not seldom a curiously felicitous one, to carry through that parallelism of the physical and psychical, which since then has come to count for more and more in the science of mind. Nor should it be forgotten that Hartley himself, for all his paternal interest in the doctrine of vibrations, was careful to keep separate from its fortunes the cause of his other doctrine of mental association. Of this the point lay in no mere restatement, with new precision, of a principle of coherence among "ideas" (which were also called by Hartley "vestiges", "types" and "images"), but in its being taken as a clue by which to follow the progressive development of the mind's powers. Holding that mental states could be scientifically understood only as they were analysed, Hartley sought for a principle of synthesis to explain the complexity exhibited not only in trains of representative images, but alike in the most involved combinations of reasonings and (as Berkeley had seen) in the apparently simple phenomena of objective perception, as well as in the varied play of the emotions, or, again, in the manifold conscious adjustments of the motor system. One principle appeared to him sufficient for all, running, as enunciated for the simplest case, thus: "Any sensations A, B, C, etc., by being associated with one another a sufficient number of times, get such a power over the corresponding ideas a, b, c, etc., that any one of the sensations A, when impressed alone, shall be able to excite in the mind b, c, etc., the ideas of the rest."