An auxiliary verb helps the main (full) verb and is also called a "helping verb." With auxiliary verbs, you can write sentences in different tenses, moods, or voices.
Auxiliary verbs are: be, do, have, will, shall, would, should, can, could, may, might, must, ought, etc.
The verb forms of be, do, and have can be used either as a main (full) verb or an auxiliary verb.
"Be" as an auxiliary verb
a.Used in progressive sentences
b.Used in passive sentences
In English grammar, the irregular verb be is an important auxiliary verb (also known as a helping verb), both in the present tense and in the past. Be has three forms in the present:
- I am
- You (We, They) are
- He (She, It) is
Be has two forms in the past:
- I (He, She, It) was
- You (We, They) were
Note that be is the only verb whose past tense changes its form to agree with the subject.
USING AM, ARE, AND IS WITH A PRESENT PARTICIPLE
A present participle is made by adding -ing to the present form of a verb. A present form of be (am, are, or is) plus the present participle describes an action that's still in progress:
- I am speaking with Miss Sunshine.
- The Griswolds are driving to California.
- Dwayne is staying with his grandfather.
Each of these sentences shows ongoing action in the present, a construction known as the present progressive.
USING WAS AND WERE WITH A PRESENT PARTICIPLE
To show continuous action in the past, we use a past form of be (was or were) with the present participle of another verb:
- I was speaking with Miss Sunshine.
- The Griswolds were driving to California.
- Dwayne was staying with his grandfather.
Remember to use was after singular subjects (singular nouns and the pronouns I, he, she, it, this, and that). Use were after plural subjects (plural nouns and the pronouns you, we, they, these, and those).
The construction that conveys a sense of ongoing action in the past is known as the past progressive.
USING A FORM OF BE WITH A PAST PARTICIPLE
To express an idea in the passive voice, we use a present or past form of be with the past participle of another verb. In the passive voice, the subject receives the action of the verb:
- The Pirates are rated number one in the region.
- The Bulldogs were beaten by the Pirates.
As a general rule, we use the passive voice when the performer of the action is unknown or is notably less important than the receiver of the action. Otherwise, we generally keep to the active voice, in which the subject performs the action of the verb:
- Sports reporters rate the Pirates number one in the region.
- The Pirates beat the Bulldogs.
Be careful not to overwork the passive voice. The active voice is usually more concise and forceful.
see more at:
https://www.thoughtco.com/present-and-past-forms-verb-be-1690359