Connectionism is the modern form of empiricist philosophy (Berkeley, 1710; Hume, 1748/1952; Locke, 1706/1977), where knowledge is not innate, but is instead provided by sensing the world.
“No man’s knowledge here can go beyond his experience” (Locke, 1706/1977, p. 83).
If recursion is fundamental to the classical approach’s rationalism, then what notion is fundamental to connectionism’s empiricism?
The key idea is association: different ideas can be linked together, so that if one arises, then the association between them causes the other to arise as well.
For centuries philosophers and psychologists have studied associations empirically, through introspection (Warren, 1921). These introspections have revealed the existence of sequences of thought that occur during thinking. Associationism attempted to determine the laws that would account for these sequences of thought. The earliest detailed introspective account of such sequences of thought can be found in the 350 BC writings of Aristotle (Sorabji, 2006):
“Acts of recollection happen because one change is of a nature to occur after another” (Sorabji, 2006, p. 54). For Aristotle, ideas were images (Cummins, 1989).
He argued that a particular sequence of images occurs because either this sequence is a natural consequence of the images, or because the sequence has been learned by habit. Recall of a particular memory, then, is achieved by cuing that memory with the appropriate prior images, which initiate the desired sequence of images.
“Whenever we recollect, then, we undergo one of the earlier changes, until we undergo the one after which the change in question habitually occurs” (Sorabji, 2006, p. 54).
Aristotle’s analysis of sequences of thought is central to modern mnemonic techniques for remembering ordered lists (Lorayne, 2007; Lorayne & Lucas, 1974). Aristotle noted that recollection via initiating a sequence of mental images could be a deliberate and systematic process. This was because the first image in the sequence could be selected so that it would be recollected fairly easily. Recall of the sequence, or of the target image at the end of the sequence, was then dictated by lawful relationships between adjacent ideas. Thus, Aristotle invented laws of association.
Laws of Association
Aristotle considered three different kinds of relationships between a starting image and its successor: similarity, opposition, and (temporal) contiguity:
“And this is exactly why we hunt for the successor, starting in our thoughts from the present or from something else, and from something similar, or opposite, or neighboring. By this means recollection occurs” (Sorabji, 2006, p. 54).
In more modern associationist theories, Aristotle’s laws would be called the law of similarity, the law of contrast, and the law of contiguity or the law of habit.
18th century British empiricists expanded Locke’s approach by exploring and debating possible laws of association. George Berkeley reiterated Aristotle’s law of contiguity, and extended it to account for associations involving different modes of sensation (Berkeley, 1710). David Hume proposed three different laws of association: resemblance, contiguity in time or place, and cause or effect (Hume, 1748/1952). David Hartley, one of the first philosophers to link associative laws to brain function, saw contiguity as the primary source of associations, and ignored Hume’s law of resemblance (Warren, 1921).
Debates about the laws of association continued into the 19th century. James Mill only endorsed the law of contiguity, and explicitly denied Hume’s laws of cause or effect and resemblance (Mill, 1829). Mill’s ideas were challenged and modified by his son, John Stuart Mill. In his revised version of his father’s book (Mill & Mill, 1869), Mill posited a completely different set of associative laws, which included a reintroduction of Hume’s law of similarity. He also replaced his father’s linear, mechanistic account of complex ideas with a “mental chemistry” that endorsed nonlinear emergence. This is because in this mental chemistry, when complex ideas were created via association, the resulting whole was more than just the sum of its parts.
Alexander Bain refined the associationism of his lifelong friend John Stuart Mill (Bain, 1855), proposing four different laws of association, and attempting to reduce all intellectual processes to these laws. Two of these were the familiar Aristotelian laws of contiguity and of similarity.