1. AUXILIARY VERBS WITH PERFECT INFINITIVE

2. The Perfect Infinitive is used with auxiliary verbs to express assumptions or speculations about the past action.  HAVE + PAST PARTICIPLE

3. It is used: 1. With should, would, might and could to form the perfect conditional in the third type of conditional clauses.  If I had seen her I should have invited her. 2. With should or ought to express unfulfilled obligation.  He should have helped her. (but he did not)  I shouldn’t have gone out. (but I did)

4. 3. With should/would like to express an unfulfilled wish.  I should like to have seen it (but it wasn’t possible). (would is used in the second and third person) 4. With could to express past unused ability.  I could have climbed the mountain (but I didn’t).

5. 5. With needn’t to express an unnecessary past action:  We needn’t have hurried. Now we are too early. 6. With may/might in speculations about past actions:  He may have come. (it is possible that he came)  He might have come. (the use of might increases the doubt)

6. 7. With must to express affirmative deduction (conclusion):  Someone must have been here recently; these ashes are still warm. 8. With can’t and couldn’t to express negative deduction:  He can’t/couldn’t have moved the piano himself.