The Chicago Guide to English Grammar, Usage, and Punctuation, Garner B.A., 2016.
The field of grammar. In its usual sense, grammar is the set of rules governing how words are put together in sentences to communicate ideas—or the study of these rules. Native speakers of a language learn them unconsciously. The rules govern most constructions in any given language. The small minority of constructions that lie outside these rules fall mostly into the category of idiom and customary usage.