May/might (not)
These refer to a present or future possibility. May is usually slightly more certain than might.
In England, unexpected guests may/might be offered some tea.
In future, people may/might not need to travel to business meetings.

May/might (not) have
The modal perfects refer to a past possibility.
Life when my parents were young may/might have been less demanding than it is now.

Must and can’t
Look at the two clauses in this sentence:
Jackie has travelled a great deal, so she must know a lot about different countries.
In the first clause, the speaker means ‘it is a fact that Jackie has travelled a great deal’.
In the second clause, the speaker means ‘I am sure Jackie knows a lot about different countries because I have worked it out from the evidence (the fact that she has travelled a great deal).’

Can’t is used to show that the speaker has considered the evidence and is sure that something isn’t true:
Jackie has only spent a few days in Canada, so she can’t know much about the country.

Must have done and can’t have done~
These are used to come to similar conclusions about the past:
Jackie must have been to South Africa because she’s got a lot of photographs of Cape Town.
Jackie’s told me about every country that she’s visited, and she’s never mentioned Egypt, so she can’t have been there.


These activities practise this Grammar: