[Modal Verb] – Lesson 5: Modal verbs – past tense forms and negatives

Modal verbs in the past

 

Modal verbs in the past
present past
should be should have been
could be could have been
will be would be
may be may have been
might be might have been
would be would have been

Modal verbs – negatives forms

Modal verbs – negative forms
positive negative
can (used for possibility)

It can happen; everything’s possible.

can’t / cannot

It can’t happen; it’s impossible.

can (used for permission)

Can I smoke here? – Yes, you can.

can’t / cannot / mustn’t

You can’t smoke here. You mustn’t smoke here.

can (used for ability)

I can play the guitar.

can’t / cannot

I can’t play the guitar.

must / have to / has to (used for obligation)

You must be there at 8 o’clock. You have to be there at 8 o’clock.

don’t have to / needn’t

You don’t have to be there at 8 o’clock.
You needn’t be there at 8 o’clock.

must (used for personal opinion, certainty)

He must be here – I can see his car.

can’t

He can’t be here – his car’s not outside.

might / may (used for personal opinion, certainty)

He might/may be late today – there’s a lot of traffic on the roads.

may not / might not

He might/may not get here on time – there’s a lot of traffic on the roads.

should (used for weak obligation / advice)

You should stop smoking because it’s unhealthy.

shouldn’t

You shouldn’t smoke so much – it’s unhealthy. You shouldn’t spend so much time watching TV.

“Had to” vs. “must have”

The modal verb “must” has two past tense forms: “had to” and “must have”. Which form we use depends on whether we want to express obligation or if we want to say how certain we are about the probability of something happening.

This table below shows us the past tense of “must” and “have to” and when to use them.

 

Must / have to
present past
When expressing obligation:
I must go. / I have to go.
When expressing obligation, the past of ‘must’ and ‘have to’ is always ‘had to’:
I had to go.
They had to be there at 2 o’clock.
When expressing a personal opinion about probability (deduction), we use ‘must’ to express that we feel something is true:
He must be here. 
It must be great.
When expressing a personal opinion in the past, we use ‘must have’, NOT ‘had to’:
He must have been here.
He had to be here.
It must have been great.
It had to be great.

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