The term linguistic performance was used by Noam Chomsky in 1960 to describe "the actual use of language in concrete situations". It is used to describe both the production, sometimes called parole, as well as the comprehension of language. Performance is defined in opposition to "competence", the latter describing the mental knowledge that a speaker or listener has of language. Part of the motivation for the distinction between performance and competence comes from speech errors: despite having a perfect understanding of the correct forms, a speaker of a language may unintentionally produce incorrect forms. This is because performance occurs in real situations, and so is subject to many non-linguistic influences. For example, distractions or memory limitations can affect lexical retrieval (Chomsky 1965:3), and give rise to errors in both production and perception. Such non-linguistic factors are completely independent of the actual knowledge of language, and establish that speakers' knowledge of language (their competence) is distinct from their actual use of language (their performance).
Background
Competence versus performance Competence is the collection of subconscious rules that one knows when one knows a language; performance is the system which puts these rules to use. This distinction is related to the broader notion of Marr's levels used in other cognitive sciences, with competence corresponding to Marr's computational level. For example, many linguistic theories, particularly in generative grammar, would propose competence-based explanations for why English speakers would judge the sentence in (1) as not "acceptable". In these explanations, the sentence would be ungrammatical because the rules of English only generate sentences where demonstratives agree with the grammatical number of their associated noun.
(1) *That cats is eating the mouse. By contrast, generative theories generally provide performance-based explanations for the acceptability of center embedding sentences like one in (2). According to such explanations, the grammar of English could in principle generate such sentences, but doing so in practice is so taxing on working memory that the sentence ends up being unparsable.
(2) *The cat that the dog that the man fed chased meowed. In general, performance-based explanations deliver a simpler theory of grammar at the cost of additional assumptions about memory and parsing. As a result, the choice between a competence-based explanation and a performance-based explanation for a given phenomenon is not always obvious and can require investigating whether the additional assumptions are supported by independent evidence. For example, while many generative models of syntax explain island effects by positing constraints within the grammar, it has also been argued that some or all of these constraints are in fact the result of limitations on performance.
Related distinctions Published in 1916, Ferdinand de Saussure's Course in General Linguistics describes language as "a system of signs that express ideas". de Saussure describes two components of language: langue and parole. Langue consists of the structural relations that define a language, which includes grammar, syntax and phonology. Parole is the physical manifestation of signs; in particular the concrete manifestation of langue as speech or writing. While langue can be viewed strictly as a system of rules, it is not an absolute system such that parole must utterly conform to langue. Drawing an analogy to chess, de Saussure compares langue to the rules of chess that define how the game should be played, and parole to the individual choices of a player given the possible moves allowed within the system of rules. In 1986, Noam Chomsky proposed a distinction similar to the competence/performance distinction, entertaining the notion of an I-Language (internal language) which is the intrinsic linguistic knowledge within a native speaker and E-Language (external language) which is the observable linguistic output of a speaker.
Performance-grammar correspondence hypothesis John A. Hawkins's Performance-Grammar Correspondence Hypothesis (PGCH) states that the syntactic structures of grammars are conventionalized based on whether and how much the structures are preferred in performance. Performance preference is related to structure complexity and processing, or comprehension, efficiency. Specifically, a complex structure refers to a structure containing more linguistic elements or words at the end of the structure than at the beginning. It is this structural complexity that results in decreased processing efficiency since more structure requires additional processing. This model seeks to explain word order across languages based on avoidance of unnecessary complexity in favour of increased processing efficiency. Speakers make an automatic calculation of the Immediate Constituent(IC)-to-word order ratio and produce the structure with the highest ratio. Structures with a high IC-to-word order are structures that contain the fewest words required for the listener to parse the structure into constituents which results in more efficient processing.
Head-initial structures In head-initial structures, which includes example SVO and VSO word order, the speaker's goal is to order the sentence constituents from least to most complex.
SVO word order SVO word order can be exemplified with English; consider the example sentences in (1). In (1a) three immediate constituents (ICs) are present in the verb phrase, namely VP, PP1 and PP2, and there are four words (went, to, London, in) required to parse the VP into its constituents. Therefore, the IC-to-word ratio is 3/4=75%. In contrast, in (1b) the VP is still composed of three ICs but there are now six words that are required to determine the constituent structure of the VP (went, in, the, late, afternoon, to). Thus, the ratio for (1b) is 3/6 = 50%. Hawkins proposes that speakers prefer to produce (1a) since it has a higher IC-to-word ratio and this leads to faster and more efficient processing.
1a. John [VP went [PP1 to London] [[PP2 in the late afternoon]] 1b. John [VP went [PP2 in the late afternoon]] [[PP1 to London]]
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