Definition:

The generative grammar stored in the brain that allows a speaker to produce language that other speakers can understand.

The concept of mental grammar was popularized by American linguistNoam Chomsky in his groundbreaking work Syntactic Structures (1957). As Binder and Smith have observed, "This focus on grammar as a mental entity allowed enormous progress to be made in characterizing the structure of languages" (The Language Phenomenon, 2013).

See also:

• Chomskyan Linguistics
• Cognitive Linguistics
• Descriptive Grammar
• Generative Grammar and Transformational Grammar
• Linguistic Competence and Linguistic Performance
• Neurolinguistics
• Psycholinguistics
• Ten Types of Grammar
• Universal Grammar

Observations:

• "Each adult speaker of a language clearly has some type of 'mental grammar,' that is, a form of internal linguistic knowledge which operates in the production and recognition of appropriately structured expressions in that language. This 'grammar' is subconscious and is not the result of any teaching."
  (George Yule, Study of Language, 2nd ed. Cambridge University Press, 1996)
• "When viewed as the representation of a speaker's linguistic competence, a grammar is a mental system, a cognitive part of the brain/mind, which, if it is one's first native language, is acquired as a child without any specific instruction. . . .
  
  "Descriptive grammars aim at revealing the mental grammar which represents the knowledge a speaker of the language has. They do not attempt to prescribe what speakers' grammars should be."
  (Victoria M. Fromin, Introduction, Linguistics: An Introduction to Linguistic Theory. Blackwell, 2000)

• "One way to clarify mental or competence grammar is to ask a friend a question about a sentence. Your friend probably won't know why it's correct, but that friend will know if it's correct. So one of the features of mental or competence grammar is this incredible sense of correctness and the ability to hear something that 'sounds odd' in a language."
  (Pamela J. Sharpe, Barron's How to Prepare for the TOEFL IBT. Barron's Educational Series, 2006)
• The Language Faculty
  "All humans are born with the capacity for constructing a Mental Grammar, given linguistic experience; this capacity for language is called the Language Faculty (Chomsky, 1965). A grammar formulated by a linguist is an idealized description of this Mental Grammar."
  (Peter W. Culicover and Andrzej Nowak, Dynamical Grammar: Foundations of Syntax II. Oxford Univ. Press, 2003)
• Implicit Knowledge of the Rules
  "A central aspect of the knowledge of a particular language variety consists in its grammar--that is, its implicit (or tacit or subconscious) knowledge of the rules of pronunciation (phonology), of word structure (morphology), of sentence structure (syntax), of certain aspects of meaning (semantics), and of a lexicon or vocabulary. Speakers of a given language variety are said to have an implicit mental grammar of that variety consisting of these rules and lexicon. It is this mental grammar that determines in large part the perception and production of speech utterances. Since the mental grammar plays a role in actual language use, we must conclude that it is represented in the brain in some way.
  
  "The detailed study of the language user's mental grammar is generally regarded as the domain of the discipline of linguistics, whereas the study of the way in which the mental grammar is put to use in the actual comprehension and production of speech in linguistic performance has been a major concern of psycholinguistics."
  (William C. Ritchie and Tej K. Bhatia, "Monolingual Language Use and Acquisition: An Introduction." The Handbook of Educational Linguistics, ed. by Bernard Spolsky and Francis M. Hult. Blackwell, 2010)

Also Known As: competence grammar, linguistic competence