University of Alberta Dictionary of Cognitive Science: Physical Symbol System Hypothesis

The physical symbol system hypothesis (Newell, 1980; Newell & Simon, 1976) is the basic hypothesis of classical cognitive science: “the necessary and sufficient condition for a physical system to exhibit general intelligent action is that it be a physical symbol system” (Newell, 1980, p. 170). By necessary, Newell means that if an artifact exhibits general intelligence, then it must be an instance of a physical symbol system. By sufficient, Newell claims that any device that is a physical symbol system can be configured to exhibit general intelligent action – that is, he claims the plausibility of machine intelligence, a position that Descartes denied.

What does Newell (1980) mean by “general intelligent action”? He means “the same scope of intelligence seen in human action: that in real situations behavior appropriate to the ends of the system and adaptive to the demands of the environment can occur, within some physical limits” (p. 170). In other words, human cognition must be the product of a physical symbol system.

References:

Newell, A. (1980). Physical symbol systems. Cognitive Science, 4, 135-183.
Newell, A., & Simon, H. A. (1976). Computer science as empirical inquiry - Symbols and search. Communications of the ACM, 19(3), 113-126.

(Added September, 2010)