Mind, Body, World- Foundations of Cognitive Science, 2013a

that can be applied to phrase markers. More modern theories of transformational
grammars have reduced the number of transformations to one, and have described
language learning as the setting of a finite number of parameters that determine
grammatical structure (Cook & Newson, 1996). Again, these grammars can be identified
in the limit on the basis of very simple input expressions (Lightfoot, 1989).
Such proofs are critical to cognitive science and to linguistics, because if a theory of
language is to be explanatorily adequate, then it must account for how language is
acquired (Chomsky, 1965).
Rationalist philosophers assumed that some human knowledge must be innate.
This view was reacted against by empiricist philosophers who viewed experience as
the only source of knowledge. For the empiricists, the mind was a tabula rasa, waiting
to be written upon by the world. Classical cognitive scientists are comfortable
with the notion of innate knowledge, and have used problems of underdetermination
to argue against the modern tabula rasa assumed by connectionist cognitive
scientists (Pinker, 2002, p. 78): “The connectionists, of course, do not believe in a
blank slate, but they do believe in the closest mechanistic equivalent, a generalpurpose
learning device.” The role of innateness is an issue that separates classical
cognitive science from connectionism, and will be encountered again when connectionism
is explored in Chapter 4.
3.6 Physical Symbol Systems
Special-purpose logic machines had been developed by philosophers in the late
nineteenth century (Buck & Hunka, 1999; Jevons, 1870; Marquand, 1885). However,
abstract descriptions of how devices could perform general-purpose symbol manipulation
did not arise until the 1930s (Post, 1936; Turing, 1936). The basic properties
laid out in these mathematical theories of computation define what is now known
as a physical symbol system (Newell, 1980; Newell & Simon, 1976). The concept
physical symbol system defines “a broad class of systems that is capable of having
and manipulating symbols, yet is also realizable within our physical universe”
(Newell, 1980, p. 136).
A physical symbol system operates on a finite set of physical tokens called symbols.
These are components of a larger physical entity called a symbol structure or
a symbolic expression. It also consists of a set of operators that can create, modify,
duplicate, or destroy symbols. Some sort of control is also required to select at any
given time some operation to apply. A physical symbol system produces, over time,
an evolving or changing collection of expressions. These expressions represent or
designate entities in the world (Newell, 1980; Newell & Simon, 1976). As a result,
the symbol manipulations performed by such a device permit new meanings to be
Elements of Classical Cognitive Science 75