Encyclopædia Britannica    Excerpt from The process of thought

At the beginning of this century the early behaviourists suggested that thought proceeded by association. The basic principles of association are similarity and contiguity, whereby an idea of something is followed by an idea of a similar or related thing.

A later, more sophisticated view that thinking proceeds according to the whole of a situation was emphasized by the Gestalt psychologists. They argued against the turn-of-the-century view that thinking proceeds by an internal process of trial-and-error, whereby a thinker imagines various responses to a stimulus, eliminates those that are inappropriate, and thus gradually comes to a final response. By contrast, the Gestalt theorists held that the solution to a problem comes as the result of a sudden insight into the nature of the problem as a whole. Around 1950, however, evidence was found that integrated these two views, by suggesting that the thinker must become familiar with a problem through trial-and-error before being able to grasp its structure as a whole.

Cognitive psychologists have pursued different paths in the study of human intelligence, including the building of computer models of human cognition. Two leaders in this field have been the American psychologists Allen Newell and Herbert A. Simon. In the late 1950s and early 1960s they worked with a computer expert, Clifford Shaw, to construct a computer model of human problem solving. Called the General Problem Solver, it could solve a wide range of fairly structured problems, such as logical proofs and mathematical word problems. Their program relied heavily on a heuristic procedure called "means-ends analysis," which, at each step of problem solving, determined how close the program was to a solution and then tried to find a way to bring the program closer to where it needed to be. Stimulated by advances in computer science, researchers have become concerned not simply with which thought element follows which, but also with operations that shift one element to the next. It is argued that these operations exploit a kind of controlled trial-and-error: in what is called a heuristic approach, the most promising avenues of solution to a problem are attempted first. Another topic of current interest concerns the motivations for thinking.

A. Newell, J.C. Shaw, and H.A. Simon pointed out the indispensability in creative human thinking, as in its computer simulations, of what they call "heuristics". A large number of possibilities may have to be examined, but the search is organized heuristically in such a way that the directions most likely to lead to success are explored first. Means of ensuring that a solution will occur within a reasonable time, certainly much faster than by random hunting, include adoption of successive subgoals and working backward from the final goal (the formula to be proved, the state of affairs to be brought about).