Modal verbs
Modal verbs are special auxilary verbs which add extra meaning to the main verb. For example, modals can express advice, necessity, and possibility.
Obligation :
must
need to
have to
it's important to
Interdiction :
it's forbidden
mustn't
it's not allowed
Advice :
should (it's a good idea)
shouldn't (it's a bad idea)
Possibility :
may (positive)
might (negative)
could / can
Permission / ability :
can
could
extras :
-The form of these modal verbs is the same for all persons.
-They don't use "to" after the verbs
-To make negative, they don't use "don't" or "doesn't", they add "not" or "n't"
-To make a question, they put the verb before I/you/...
-Exception = have to
the form of "have to" change in the same way as the verb "have"
they use "do" or "does" to make a question and "don't" and "doesn't" to make negatives
-Tense :
could (past) / can (present) / will be able to (future)
Had to (past) / must (present) / will have to (future)
may have (past) / may / may have to (future)