Auxiliary verb

Definition: Auxiliary verbs are used together with a main verb to give grammatical information and therefore add extra meaning to a sentence, which is not given by the main verb.
Be, Do and Have are auxiliary verbs, they are irregular verbs and can be used as main verbs.
Modal verbs are also auxiliary verbs, but will be treated separately, these are can, could, may, might, must, shall, should, will, and would.
To be: Be is the most common verb in the English language. It can be used as an auxiliary and a main verb. It is used a lot in its other forms.

Present tense form	Past tense form
am/is/are	was/were

Uses:

Am/Is/Are:

Question	Positive Statement	Negative Statement
Singular
Am I?	I am (I'm)	I am not (I'm not)
Are you?	You are (You're)	You are not (You're not/You aren't)
Is he/she/it?	He/she/it is (He's/She's/It's)	He/she/it is not (He/she/it isn't// He/she/it's not)
Plural
Are we?	We are (We're)	We are not (We aren't/We're not)
Are you?	You are (You're)	You are not (You aren't/You're not)
Are they?	They are (They're)	They are not (They aren't/They're not)

Examples:

Note: The auxiliary verb 'be' can be followed either by the -ed form or by the -ing form.

To do: The verb do is one of the most common verbs in English. It can be used as an auxiliary and a main verb. It is often used in questions.

Uses:

Do / Does

Question	Positive Statement (spoken)	Negative Statement (spoken)
Singular
Do I?	I do	I do not (I don't)
Do you?	You do	You do not (You don't)
Does he/she/it?	He/she/it does	He/she/it does not (He/she/it doesn't)
Plural
Do we?	We do	We do not (We don't)
Do you?	You do	You do not (You don't)
Do they?	They do	They do not (They don't)

Examples:

	Do	Does
Question - ?	"Do you always take the bus to work?"	"Does she ever do her homework on time?"
Positive Answer - Yes	"Yes I do."	"Yes she does."
Negative Answer - No	"No I don't."	"No she doesn't."

Note: The auxiliary verb 'do' is always followed by the base form (infinitive).

To have: Have is one of the most common verbs in the English language. Have is used in a variety of ways.

Uses:

Have/Has

Question	Positive Statement (spoken)	Negative Statement (spoken)
Singular
Have I?	I have (I've)	I have not (I haven't/I've not)
Have you?	You have (You've)	You have not (You haven't/You've not)
Has he/she/it?	He/she/it has (He/she/it 's)	He/she/it has not (He/she/it hasn't)
Plural
Have we?	We have (We've)	We have not (We haven't/We've not)
Have you?	You have (You've)	You have not (You haven't/You've not)
Have they?	They have (They've)	They have not (They haven't/They've not)

Have is often used to indicate possession (I have) or (I have got).

Examples:

	Have	Have got
Question - ?	"Do you have a car?" or "Have you a car?"	"Have you got a car?"
Positive Answer - Yes	"Yes I have a car."	"Yes I've got a car."
Negative Answer - No	"No I don't have a car."	"No I haven't got a car."

Have is also used to indicate necessity (I have to) or (I have got to).