some quotes from Newell and Simon's paper "Computer Science as Empirical
Inquiry: Symbols and Search" which
define the essential ideas of the Physical Symbol System Hypothesis:
The hypotheses states:
"A physical symbol system
has the necessary and sufficient means for intelligent action."
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."
"Two notions are central
to this structure of expressions, symbols, and objects: designation
"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
involve completeness and closure. (1) A symbol may be used to
designate any expression whatsoever. That is, given a symbol,
it is not prescribed a priori what expressions it can
designate. This arbitrariness pertains only to symbols; the symbol
tokens and their mutual relations determine what object is designated
by a complex expression. (2) There exist expressions that designate
every process of which the machine is capable. (3) There exist
processes for creating any expression and for modifying any expression
in arbitrary ways. (4) Expressions are stable; once created they
will continue to exist until explicitly modified or deleted.
(5) The number of expressions that the system can hold is essentially