Foundations Of Cognitive Science


A grammar is a system of rules that can be used to specify the potentially infinite set of expressions that make up a language.  A grammar for a natural language describes a speaker-hearer’s ideal knowledge of a language, that is, competence.  However a grammar does not provide any information about the use of language – why a particular sentence was uttered (and not some other grammatical expression).  A theory of language use is a theory of language performance.

Performance is not part of a theory of competence because many factors that are not part of a grammar can affect language use.  Such factors include “such grammatically irrelevant conditions as memory limitations, distractions, shifts of attention and interest, and errors (random or characteristic) in applying knowledge of the language in actual performance (Chomsky, 1965, p. 3).

One way of thinking about the difference between competence and performance is by applying parts of the tri-level hypothesis (Dawson, 1998).  In particular, a theory of competence is a formal account of potential behavior that is formulated at the computational level of analysis.  In contrast, a theory of performance is most likely to be constructed at the algorithmic level; it will be a working model that will explain algorithmic details (e.g. latencies of processing), a kind of theory developed in psycholinguistics or in the psychology of language (Jakobovits & Miron, 1967; Marslen-Wilson, 1989; Pavio & Begg, 1981).


  1. Chomsky, N. (1965). Aspects Of The Theory Of Syntax. Cambridge, MA: MIT Press.
  2. Dawson, M. R. W. (1998). Understanding Cognitive Science. Oxford, UK: Blackwell.
  3. Jakobovits, L. A., & Miron, M. S. (1967). Readings In The Psychology Of Language. Englewood Cliffs, NJ: Prentice-Hall.
  4. Marslen-Wilson, W. (1989). Lexical Representation And Process. Cambridge, MA: MIT Press.
  5. Pavio, A., & Begg, I. (1981). Psychology Of Language. Englewood Cliffs, NJ: Prentice-Hall.

(Added September 2010)