Modal Verbs are a tricky part of English grammar. Firstly, I’d like to answer a question which is rarely asked: how do we define a modal verb?
What is a modal verb?
Modal verbs are verbs which
a) have no infinitive form, gerund form, or 3rd form (and so they can’t be used in present perfect)
b) have no ‘s’ added in 3rd person present simple
c) are followed by verbs in the infinitive (without to)
These include: SHOULD/SHOULDN’T, MUST/MUSTN’T, CAN/CAN’T, WOULD/WOULDN’T, WILL/WON’T, COULD/COULDN’T, SHALL/SHAN’T, MAY, MIGHT
He shouldn’t smoke so much.
She can come too.
He mustn’t do that while he is here.
Modals of obligation
‘Have to’ is NOT a modal verb, but it is often taught to students at the same time as ‘modal verbs’ because it’s meaning is connected to obligations and necessities, like other modal verbs. In this elementary lesson we find out the differences between basic modal verbs.
MUST / HAVE TO (obligation)
SHOULD / SHOULDN’T (opinion)
DON’T HAVE TO (not necessary)
MUSTN’T (not allowed)
Modals of deduction
However, not all modals deal with obligation and permission. Many modals deal with deductions. Namely, whether something is definitely true, might be true, or is certainly not true.
He must be French (definitely true)
He might be French (50/50)
He can’t be French (definitely not true)
And in the past tense
Napoleon must have been French (definitely was true)
Napoleon might have been French (50/50)
Napoleon can’t have been French (definitely wasn’t true)
The following lesson deals with these modal verbs:
All modal forms
I have also made a lesson where I deal with both modal verbs of obligation, as well as those of deduction. I hope this helps to resolve any remaining confusion
Now please test your knowledge of modal verbs with the following quiz
Modals verbs in all 4 aspects
The basic structure is the following:
Modal + infinitive (could do)
Modal + be + ____ing (could be doing)
Modal + have + 3rd (could have done)
Modal + have + been + ____ing (could have been doing)
He must have been drinking last night because he got arrested.
When he arrived, we should have been waiting for him.
They might have been sleeping as they didn’t hear me come in.
If you enjoyed learning about modal verbs, please browse some of the other lessons and quizzes on my site