You have already encountered three auxiliary (or helping) verbs: be, do, and have. They are conjugated and used with another verb to change that verb’s meaning or tense:
I go → I am going (changed to in progress or incomplete)
you sing → do you sing? (changed to a question)
she makes → she has made (changed to the present perfect tense)
There are several other auxiliary verbs you should know. Note that many of the auxiliary verbs cannot be used in all tenses. And in some cases, you have to change to a different verb to form a specific tense. The following examples will be conjugated with the third-person pronoun he:
to be able to
to be supposed to
Present
is able to
is supposed to
Past
was able to
was supposed to
Present Perfect
has been able to
has been supposed to
Past Perfect
had been able to
had been supposed to
Future
will be able to
will be supposed to
Future Perfect
will have been able to
will have been supposed to
can
to have to
Present
can
has to
Past
could OR was able to
had to
Present Perfect
has been able to
has had to
Past Perfect
had been able to
had had to
Future
will be able to
will have to
Future Perfect
will have been able to
will have had to
may
must
Present
may
must
Past
might
had to
Present Perfect
N/A
has had to
Past Perfect
N/A
had had to
Future
N/A
will have to
Future Perfect
N/A
will have had to
ought to
should
Present
ought to
should
Past
N/A
N/A
Present Perfect
N/A
N/A
Past Perfect
N/A
N/A
Future
N/A
N/A
Future Perfect
N/A
N/A
to want to
to need to
Present
wants
needs to
Past
wanted
needed to
Present Perfect
has wanted
has needed to
Past Perfect
had wanted
had needed to
Future
will want
will need to
Future Perfect
will have wanted
will have needed to
Auxiliary verbs like these are followed by an infinitive:
I can go.
I want to go.
You must learn.
You have to learn.
We should help.
We need to help.
He can drive.
He ought to drive.
When you use some of the auxiliaries with a verb, you tell to what degree of obligation someone has to carry out the action of the verb. Look at the sentences below. The first one shows the least degree of obligation. This is something someone doesn’t have to do. The last sentence shows the greatest degree of obligation. This is something that someone absolutely must do.
“We may return the books.” (Least obligation. It’s our choice.)
“We can return the books.” (Little obligation. It’s our choice.)
“We are able to return the books.” (Little obligation. We have the ability to do this.)
“We need to return the books.” (Slight obligation.)
“We ought to return the books.” (Little obligation, but this would be a good idea.)
“We should return the books.” (Little obligation, but this would be a good idea.)
“We are supposed to return the books.” (Some obligation. Someone has suggested we do this.)
“We must return the books.” (Greatest obligation. It is our duty to do this.)
“We have to return the books.” (Greatest obligation. It is our duty to do this.)
When you add an auxiliary to a sentence, use the same tense for the auxiliary as that of the original verb. For example: “Celeste found (past tense) a recent biography.” When you add have to to that sentence, you say, “Celeste had to (past tense) find a recent biography.”
