Grammar rules also dictate how verbs change based on the tense. In English, for example, the verb ''to be'' changes based on tense: I was (past), I am (present), I will be (future). Some languages have more tenses than others, but most change the verbs based on the tense being used as well as the subject.

In the strictest sense, grammar does not include word usage. Grammar pertains to how words change their forms and how they are organized to make structurally sound sentences. Usage involves choosing words with the correct meaning given the context of a sentence.