First,
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 and
interpretation."
"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."
"Additional requirements 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
unbounded."
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