- Descriptive grammar: the systematic study and description of a language. Descriptive grammar refers to the structure of a language as it is actually used by speakers and writers.
- Prescriptive grammar: a set of rules and examples dealing with the syntax and word structures of a language, usually intended as an aid to the learning of that language. Prescriptive grammar refers to the structure of a language as certain people think it should be used.
Both kinds of grammar are concerned with rules--but in different ways. Specialists in descriptive grammar (called linguists) study the rules or patterns that underlie our use of words, phrases, clauses, and sentences. On the other hand, prescriptive grammarians (such as most editors and teachers) lay out rules about what they believe to be the “correct” or “incorrect” use of language.
For more information, see What Is Grammar?