Verb “to be” (am / is / are)

The verb 'to be' is one of the most important verbs in English. We use three forms in the present tense: am, is, and are. Use am only with the pronoun I (I am a student). Use is with singular subjects: he, she, it, and any single person or thing (She is kind. The dog is small.). Use are with plural subjects and also with you (whether one person or many): you are, we are, they are. In negative sentences, add not after the verb: I am not tired, He is not (or isn't) here, They are not (or aren't) ready. English also uses contractions in everyday speech and informal writing: I'm, you're, he's, she's, it's, we're, they're for affirmative, and isn't / aren't for negative (there is no contraction for am not in standard English). The form of 'to be' must always agree with its subject — this is called subject-verb agreement. For example: My brother is ten years old and my sisters are twelve.