The Physical Symbol System Hypothesis: Status and Prospects

I analyze some of the attacks against the Physical Symbol System Hypothesis—attacks based on the presumed need for symbolgrounding and non-symbolic processing for intelligent behavior and on the supposed non-computational and “mindless” aspects of brains. The physical symbol system hypothesis (PSSH), first formulated by Newell and Simon in their Turing Award paper,1 states that “a physical symbol system [such as a digital computer, for example] has the necessary and sufficient means for intelligent action.” The hypothesis implies that computers, when we provide them with the appropriate symbol-processing programs, will be capable of intelligent action. It also implies, as Newell and Simon wrote, that “the symbolic behavior of man arises because he has the characteristics of a physical symbol system.” Newell and Simon admitted that The hypothesis could indeed be false. Intelligent behavior is not so easy to produce that any system will exhibit it willy-nilly. Indeed, there are people whose analyses lead them to conclude either on philosophical or on scientific grounds that the hypothesis is false. Scientifically, one can attack or defend it only by bringing forth empirical evidence about the natural world. Indeed, many people have attacked the PSSH. Their arguments cluster around four main themes. One theme focuses on the presumption that computers can only manipulate meaningless symbols. Intelligence, some people claim, requires more than formal symbol manipulation; it requires some kind of connection to the environment through perception and action in order to “ground” the symbols and thereby give them meaning. Such connectedness is to be achieved through what some of its proponents call “embodiment.” Intelligence requires a physical body that senses and acts and has experiences. 1 Allen Newell and Herbert A. Simon, “Computer Science as Empirical Inquiry: Symbols and Search,” Communications of the ACM. vol. 19, No. 3, pp. 113-126, March, 1976. Available online at: http://www.rci.rutgers.edu/∼cfs/472 html/AI SEARCH/PSS/PSSH1.html M. Lungarella et al. (Eds.): 50 Years of AI, Festschrift, LNAI 4850, pp. 9–17, 2007.