Well-formedness
In linguistics, well-formedness is the quality of a clause, word, or other linguistic element that conforms to the grammar of the language of which it is a part. Well-formed words or phrases are grammatical, meaning they obey all relevant rules of grammar. In contrast, a form that violates some grammar rule is ill-formed and does not constitute part of the language.
A word may be phonologically well-formed, meaning it conforms to the sound pattern of the language. For example, the nonce word wug coined by Jean Berko Gleason is phonologically well-formed, so informants are able to pluralize it regularly. A word, phrase, clause, or utterance may be grammatically well-formed, meaning it obeys the rules of morphology and syntax. A semantically well-formed utterance or sentence is one that is meaningful. Grammatical well-formedness and semantic well-formedness do not always coincide. For example, the following sentence is grammatically well-formed, but has no clear meaning.
The concept of well-formedness was developed in generative grammar during the twentieth century. Sometimes native speakers of a language do not agree whether a particular word, phrase, or clause is well-formed. This problem of gradient well-formedness, uncertainty about the well-formedness of a particular example, is a problem for generative linguistics, which assumes that grammar follows some universal patterns that should not vary among speakers.