Modal verbs

Deduction and speculation

We use might (not) + infinitive to say that something now or in the future is possible.

• Elvis might be alive.
  (= It's possible that Elvis is alive.)

• Elvis might not be dead.
  (= It's possible that Elvis is not dead.)
  
  
• Elvis might live in New York.
  (= It's possible that Elvis lives in New York.)

We use must, might or can't + infinitive to speculate about situations in the present.

• He must be alive.
  (= I am sure he is alive.)

• He might be alive.
  (= I think it is possible he is alive.)

• He can't be alive.
  (= I am sure he isn't alive.)

We can also use might + infinitive to say that a future situation or action is possible.

• I might go to New York in August.
  (= It's possible I'll go to New York in August.)

We can use must, might or can't + be + verb + -ing to speculate about activities in progress in the present and about temporary situations in the present.

• Mary might be having lunch.
  (= It's possible that Mary is having lunch.)

Use must, might or can't + have + past participle to speculate about the past.

• She must have been very unhappy.
  (= I am sure that she was unhappy.)

• She might have arrived late.
  (= It's possible that she arrived late.)

• He can't have heard the phone.
  (= I am sure that he didn't hear the phone.)