# Use of Perfect Infinitive

1 He is understood to have left India for good last year.

2 The scientist claim to have discovered cure for AIDS and the medicine will be put on sale very soon.

3 He pretended to have lost her contact number.

4 We hope to have finished the project by the end of march.

5 I'm sorry to have disturbed you.

In all these sentences its use "to have", but purpose is different. For example in 4 it uses for future perspective while in 3 for past. Can someone explain the concept of "to have"? I find it difficult where to use "to have" or not. For example I would write 4th sentence as "We hope to finish the project by the end of march (if I haven't seen this sentence in my book). I also read that we can use perfect infinitive construction to talk about plans which didn't happen. But this rule doesn't follow with 5 sentence.

Thank you

• For example I would write 4th sentence as "We hope to finish the project by the end of march" - This is actually perfectly fine!!! There's nothing wrong with this sentence. Sentence 4 is also fine but it's not the only correct construction. The two sentences have slightly different implications but they say, essentially, the same thing. :) Sep 12, 2015 at 18:23

Perfect infinitive is used to indicate the completeness of the event or process relative to the time of some other indicator.

He pretended to have lost...

In the past ('pretended') he was giving an impression that at that time (at the time of giving the impression) he already did not have the number. We might imagine hearing him saying, "I have lost the number." That is the idea of his pretending.

We hope to have finished the project by the end of March. >>>

We entertain a notion that when the end of March comes, the project will have been complete (for some time then). The difference between that and

We hope to finish the project by end of March. >>>

is that in the latter sentence our finishing of the project will coincide with the end of March, or so we hope. In the 'to have finished' case, the temporal relation is only that the project is going to be finished before the end of March. In other words:

We hope to have finished by the end == We hope to finish before the end.

As far as "I am sorry to have disturbed" goes, same explanation. "I am" indicates Present Tense, i.e. now. You could say "I am sorry to disturb you", and that implies that you think you are disturbing them now. If the act of disturbing them happened prior to your admitting that you are sorry, then the act of disturbing is in the past. In order to refer to the past with relation to other time in a construct which otherwise uses "to+infinitive", the "to+have+PastParticiple" (Perfect Infinitive) is used.

• "I did not want her to have spent all her money at the fair yesterday." but book say it should be "I did not want her to spend all her money at the fair yesterday." Can you please explain this? @victor Bazarov Sep 15, 2015 at 13:24
• I think it's the case of KISS principle (Keet It Simple, Silly). Don't use Perfect tense when Indefinite is sufficient. Sep 15, 2015 at 13:27