might have/may have

For something that happened in the past, we can use may have or might have.

The police think he might have seen the robbery and are looking for him.

What if there is a specified time in the sentence above ? Can we still use might/may have ?


The use of ‘may’ or might’ with the perfect infinitive (might have/may have seen) both refer to the past. The difference between ‘may’ and ‘might’ is a question of degree. ‘May’ suggests a possibility and ‘might’ a probability - less likely/possible. The reference to a definite time doesn’t affect either ‘may’ or ‘might’.


The police think he might have seen the robbery on Sunday and are looking for him.

Does that mean the sentence on the above is correct?
Does the phrase “must has” is correct?
May I know if must have is also doesn’t affected by a definite time?

Please correct me if I have made a mistake.


1 Yes.

2 No. ‘Must’ is followed by the present infinite ‘have’ or perfect infinitive ‘must have had’.

3 ‘Must have’ isn’t affected.


Thanks a lot.

In my, learner’s, opinion the statement which I put into red isn’t quite correct and Whoami412 needs additional peace of information.
The perfect conditional that is formed by using the modals may or might as the first auxiliaries and the perfect infinitive, I personally use for events that might have happened and not happened in the past for sure.
So the perfect conditional is used for statements that are not necessarily 100% true. The event depends on some conditions.
If he was there he could have seen what happened. But we don’t know whether he was there or not.
Though he was there even, he might have been lighting his cigarette and not seen the event in which the police are interested, at all.
In your sentence " The police think he might have seen…", the police are (“is” is used on the other side of the pond) not sure whether he saw the event (robbery) that happened in the past.

The past can be either definite or indefinite.
He might have been there.
He might have been there last night (Friday, at 5 o’clock, etc).