The two types of auxiliary verb are primary verbs and modal verbs. The primary verbs are behave, and do which come in three forms: ending in –s formpast form, and the past participle form as shown in the following table.

 

Primary verbs

be

have

do

-s form

is

has

does

Past form

was/were

had

did

Past participle

been

had

done

 

 

 

 

Modal verbs

 

 

 

will

can

may

shall

would

could

might

should

must

ought to

used to