Any native speaker of a language can be said to know the grammar of his/her own language, they know how to form and interpret any expression. However, this grammatical knowledge is subconscious. Native speaker have grammatical competence in their native language. This means that they have tacit knowledge of the grammar of their own lang. We have to make a difference between competence (the fluent native speaker's tacit knowledge of his lang) and performance (what people actually say and understand, the use of the language).
Criteria of adequacy
Basically, the criteria of adequacy are 2: descriptive adequacy (universality) and explanatory adequacy.
1. A grammar is descriptively adequate if it correctly describes whether a sequence of words is or isn't grammatical and also correctly describes what interpretation(s) this sequence has. 1.1. The goal of a descriptive linguist is to devise particular grammars of particular languages, while that of a theoretical linguist is to devise a theory of grammar. This is a set of hypotheses about the nature of possible and impossible grammars of natural languages and about the inherent properties that natural langs do and don't possess. An adequate theory of grammar must satisfy the criterion of adequacy known as universality. This means that a theory of grammar must enable us to devise a descriptively adequate grammar for every natural lang. The main goal of Generative Grammar is to build a theory of Universal Grammar.
2. This theory of UG will not only list the universal properties of natural lang grammars, but also explain the relevant properties --i.e. why grammar have the properties they do. This requirement is referred to as explanatory adequacy.
According to Chomsky, the most plausible explanation for uniformity and rapidity lies in that the course of acquisition is determined by a biologically endowed innate language faculty within the brain, which provides children with a genetically transmitted set of procedures for developing a grammar on the basis of their linguistic experience (the speech input they receive). The hypothesis that the course of lang acquisition is determined by an innate language faculty is known as the innateness hypothesis. The major tenets of this hypothesis are:
1. The innate language faculty is unique to humans. 2. All humans possess this ability of lang acquisition. 3. The uniformity character suggests that children have a genetic guidance in the task of building a grammar of their native lang. 4. Despite performance errors in the input, children acquire a competence grammar, which again points to the fact that the acquisition ability must be genetically determined. 5. Although no special care is taken to teach them, children acquire languages successfully, which again supports the genetic character of lang acquisition.
We have claimed that children have a genetically endowed language faculty. If so, what are the defining properties of the language faculty? The lang faculty must include a set of principles of Universal Grammar, in the sense that the lang faculty must be such as to allow the child to develop a grammar of any natural lang on the basis of a sufficient speech input. If these principles are universal their application in one language should reveal evidence of their application in other langs. The underlying rule to construct a particular structure in one language will be part of a general principle of UG.
(1) a. Mary will tell me the truth.
b. Will Mary tell me the truth?
(Move the second word in a sentence in front of the first word)
(2) a. The girl in the corner will tell me the truth.
b. *Girl the in the corner....?