stty consulting › our future

Physical Symbol System Hypothesis

Newell and Simon (1976) define the Physical Symbol System Hypothesis as:

"A physical symbol system has the necessary and sufficient means for intelligent action."

Newell and Simon (1976) state a physical symbol system "consists of a set of entities, called symbols, which are physical patterns that can occur as components of another type of entity called an expression (or symbol structure). Thus, a symbol structure is composed of a number of instances (or tokens) of symbols related in some physical way (such as one token being next to another). At any instant of time the system will contain a collection of these symbol structures. Besides these structures, the system also contains a collection of processes that operate on expressions to produce other expressions: processes of creation, modification, reproduction and destruction. A physical symbol system is a machine that produces through time an evolving collection of symbol structures. Such a system exists in a world of objects wider than just these symbolic expressions themselves."

The Physical Symbol System Hypothesis unlike the traditional methods of AI that rely on representational formalisations and search based reasoning methods distinguishes between the knowledge patterns formed and the method used to represent them. By separating the arrangement of symbols and the medium used, knowledge or wisdom must be able to be represented physically. "If intelligence is derived form the patterns the structure of the patterns and symbol system, regardless of the medium that successfully implement the correct patterns and processes with achieve intelligence." (G. Luger 2002)

C.F. Schmidt notes that there are two notions are pivotal to this method of representing knowledge through expressions, symbols, and objects:

"Designation. An expression designates an object if, given the expression, the system can either affect the object itself or behave in ways dependent on the object. ... In either case, access to the object via the expression has been obtained, which is the essence of designation.

Interpretation. The system can interpret an expression if the expression designates a process and if, given the expression, the system can carry out the process. ...Interpretation implies a special form of dependent action: given an expression the system can perform the indicated process, which is to say, it can evoke and execute its own processes from expressions that designate them." (Newell and Simon, 1976)

Designation works towards the premise that knowledge is not uniquely attributable to one process, task or domain. Obviously there will be exceptions to this rule, but they are in the minority in my opinion. For example my limited knowledge of shed building could easily be applied to constructing a Doll's house for my daughters. The importance of designation is that for the system to display true signs of intelligence it must react to external simulation and possibly, as in the Turing test, interact with other intelligent beings.

C.F. Schmidt explains that "A symbolic expression designates some object if the system's behaviour with respect to this outer world is dependent on the object which is referenced. Intuitively, the idea is that intelligent action is realized in relation to some external world. Thus, to reason about how to act in this world requires that the system of symbol structures in some sense represent aspects of this external world."

Interpretation is the idea that a symbol or expression could be a representation of a process to be carried out. The system would interpret the expression, or expressions, and then through the application of actions perform a task. This could extend from the simple courteous language responses of "please" and "thank-you" to questions to the complete erection of a 'flat-packed' shed.

When the idea interpretation is combined with genetic programming technique is can be easier understood the power of this method. The combination would allow for virtually endless mutation and crossovers to create new expressions. The greater the interaction with external forces the greater the potential of the system.

Newell and Simon 's Physical Symbol System Hypothesis implies that if a physical symbol system is designed and organised well enough can exhibit intelligence in the same manor as seen in human action. This would mean that anything capable of storing and processing a physical symbol system is intelegent. "Computers are capable of implementing any effectively described symbolic process. Does it not follow that a properly programmed digital computer will achieve intelligence?" (Machtey & Young 1979)

C.F. Schmidt "AI and Search -Table of Contents"

Allen Newell and Herbert Simon (1976)" Computer Science as Empirical Enquiry: Symbols and Search"

Luger G. (2002) "Artificial Intelligence. Structures and Strategies for Complex Problem Solving" - Addison Wesley

Machtey M. and Young P. (1979) "an introduction to the general theory of algorithms" - Amsterdam: Holland