The Physical Symbol System Hypothesis

The fundamental principle is the identification of intelligence with the functioning of a rule-governed symbol-manipulating device. It has been most explicitly stated by Newell and Simon:

A physical symbol system has the necessary and sufficient means for general intelligent action. . . . By 'general intelligent action' we wish to indicate the same scope of intelligence we see in human action: that in any real situation behavior appropriate to the ends of the system and adaptive to the demands of the environment an occur, within some limits of speed and complexity.^[11]

This "physical symbol system hypothesis" presupposes materialism—the claim that all of the observed properties of intelligent beings can ultimately be explained in terms of lawful physical processes. It adds the claim that these processes can be described at a level of abstraction in which all relevant aspects of a physical state can be understood as the encoding of symbol structures and that the activities can be adequately characterized as systematic application of symbol manipulation rules.

The essential link is representation —the encoding of the relevant aspects of the world. Newell lays this out explicitly:

An intelligent agent is embedded in a task environment; a task statement enters via a perceptual component and is encoded in an initial representation . Whence starts a cycle of activity in which a recognition occurs . . . of a method to use to attempt the problem. The method draws upon a memory of general world knowledge . . . . It is clear to us all what representation is in this picture. It is the data structures that hold the problem and will be processed into a form that makes the solution available. Additionally, it is the data structures that hold the world knowledge and will be processed to acquire parts of the solution or to obtain guidance in constructing it.^[12] [emphasis in original]

Complete and systematic symbolic representation is crucial to the paradigm. The rules followed by the machine can deal only with the symbols, not their interpretation.