Be

The verb be is one of the three primary verbs that are important in English in the construction of aspect (progressive/continuous, perfect), voice (passive), and of negative, interrogative and emphatic forms of full verbs. It is also the commonest verb in the English language.

It can be used both as the existential verb (I think, therefore I am) and as a copular verb (My daughter is a teacher).

Auxiliary verb
As an auxiliary verb, it is used in the construction of the progressive/continuous aspect (progressive auxiliary ) - My daughter is/was living in Manchester - and of the passive voice (passive auxiliary ) - Luke was promoted last week.

Forms

 * be, am, is/isnt, are/aren't, was/wasn't, were/weren't, been, being.

Contractions
The verb be can usually be contracted in more than one way for the affirmative, negative and interrogative:
 * I am: I'm - aren't I? - I'm not (see Note 1 below)
 * you are: You're - aren't you? - you're not or you aren't
 * s/he/it is: s/he/it's - isn't s/he/it? - s/he/it's not or s/he/it isn't
 * we are: we're - aren't we? - we're not or we aren't
 * they are: they're - aren't they? - they're not or they aren't

Note 1: I'm not is the standard contraction. I aren't is not correct. Likewise, for questions, aren't I? is the standard contraction, although amn't I? may be used in some dialects.

Ain't
See main article Ain't.

The contraction ain't for am not; are not and is not, while widespread in the 18th century as a contraction for am not, is still normal in many dialects and informal speech. It is not standard English, however, and should not be used in formal or written contexts.