English Grammar

Logical Conclusions – Events in the past:

Remember that “must” is a modal. “Must” followed be the verb word have and a participle expresses a logical conclusion based on evidence. The conclusion is about an event that happened in the past.

Remember that an observation in the present may serve as the basis for a conclusion about something that happened in the past. For example, “Here is a message on my desk.” It may be conclusion that “My friend must have called last night.”

    Examples:

         1.       Incorrect: The streets are wet; it should have rained last night.

        Correct: The streets are wet; it must have rained last night.

         2.       Incorrect: This pen won’t write; it can have run out of ink (in the past).

        Correct: This pen won’t write; it must have run out of ink (in the past).

        3.       Incorrect: The ring that I was looking at is gone; someone else must buy it.

        Correct: The ring that I was looking at is gone; someone else must have bought it.

        4.       Incorrect: He does not have his keys; he must locked them in his car.

        Correct: He does not have his keys; he must have locked them in his car.

        5.       Incorrect: I don’t see Martha anywhere; she must be left early.

                Correct: I don’t see Martha anywhere; she must have left early.

         6.      Incorrect: The theory of continental Drift assumes that there must long-term climate  

                                  changes in many areas during the past.

               Correct: The theory of continental Drift assumes that there must have been long-term 

                             climate changes in many areas during the past.

         7.       Incorrect: When the weather becomes colder we know that air mass must originated in 

                                    the Arctic rather than over the Gulf of Mexico.

         Correct: When the weather becomes colder we know that air mass must have originated 

                           in the Arctic rather than over the Gulf of Mexico