In linguistics, the term usage relates to the habits of word use among a language’s native speakers. So a usage error might be the misuse of a word in place of another or the use of an idiom outside its conventional meaning. Grammar relates to the functions of words, the construction of sentences, and how words combine to make sentences. So, for example, the misuse of a comma, an incorrect verb inflection, and a misplaced adverbial phrase are grammar errors. Usage evolves continually, often rapidly, and is subjective in many ways. Grammar is more technical and tends to evolve more slowly.
Usage often appears where use would make more sense, but we won’t get into that here.
Examples
These writers correctly use usage to mean habit of word use:
Usage of the word became more complex with the dawn of the gay-rights movement. [NPR]
I explained that “gotten” is a Renaissance usage found throughout Shakespeare; he uses “ungotten” too. [Guardian]
But the word I’m looking for, apparently, is downsize, a nasty bit of jargon which has crept into ordinary usage. [Canberra Times]
And these writers use the word grammar well:
This charge of “word abuse” brings to mind the debate about when the rules of grammar should bend to meet the demands of the “mob.” [National Post]
Note that even then, however, he preserved the lack of grammar that is central to Dylan’s best work. [Irish Times]
Grammar books indicate quotation marks qualify the meaning of a term and thus Ryan — in Ayn Rand fashion — disputes that health care is a right. [Washington Post]
