a) He turned angry enough to kill.
b) He had turned angry enough to kill.
c) He turned angry enough to have killed.
d) He had turned angry enough to have killed.
[Mav in Black. Me in Blue]
My current understanding is as following:
//Examples a) and b) are present infinitives though.
a) "He turned angry enough to kill." = Maybe he killed (or maybe not); he was angry enough to kill. (This is almost self-explanatory.)
Yes, I’d say so.
b) "He had turned angry enough to kill." = It's the same as the first sentence, only in Past Perfect.
Yep. I take it you are clear enough up to here.
"So far, so good", but here comes the Perfect Infinitive.
c) "He turned angry enough to have killed."
Did he, or did he NOT kill in the end?
It’s not implicit in the sentence whether he did or not. In the following example, it’s clear that he didn’t: "He turned angry enough to have killed if he was pushed much further.”
Some people would prefer the past perfect in this sentence.
My point – that all of these sentences were possible – was to emphasise that it is the context that counts. Isolated sentences without context don’t tell the full story.
The perfect form suggests (to me) that it actually happened, but if I remember correctly, the Perfect Infinitive has something to do with the 'imaginary past', where the actions did NOT complete. (Eg.: 'He was to have come.' implies that he did not come.
That’s right, and “He was to have come, but he was caught up” is even more revealing.
Or 'I hoped to have asked you out for a dinner one day.' implies that it has never happened.) Am I right?
Yes. But the beauty of sentences is that you can make them longer to add important qualifying information, or put the sentence in a paragraph and reveal all! In fact, I would go so far as to say that there is far too much “Is this sentence correct?” on this site, and not enough Discourse Analysis. This is not meant as a criticism of you. It’s an observation on the apparent belief that the sentence is the unit of meaning, and must be self-contained – whereas almost no one in real life tries to cram all of their meaning into one sentence.
To say that a sentence is correct, is simply to say that there are no obvious grammatical mistakes in it, that it could be placed within a context to give a clear meaning – not that it is a self-contained semantic unit from which the meaning is easily extracted.
Or I am right, BUT 'imaginary past' is only one usage of the Perfect Infinitive, and in other situation the Perfect Infinitive 'behaves' differently. If so, how? Might I ask you to make these things, you know, crystal clear?
The perfect infinitive behaves differently if the writer chooses to make it do so. To get his/her message across, s/he has a wide choice of tools which can be used in different combinations, and which still get the same job done.
d) "He had turned angry enough to kill."
I would be a bit surprised if it were that simple only to be the Past Perfect 'version' of the example c).
Well, it is c) with one the tenses changed to the past perfect. That would make it the appropriate phrase to use if “he had turned” rather than “he turned” was indicated by the context. Why does this relationship surprise you?
But I agree that there are other ways of conceptualising d) rather than as the “past perfect version of c)”.
And last, can the Perfect Infinitive be used after Present Perfect?
Yes. You generally wouldn’t write, “He has turned angry enough to have killed”. But it could be made to work:
A: “Do you think John could have killed this man yesterday?”
B: “Well, over the last week, he has turned angry enough to have killed this man yesterday.”
I came across a sentence in a fan fiction, where they were used together: "He can be such a stick in the mud. Although, I guess he's had to have been able to stay alive out there for many years." I admit I don't really understand this structure, though I should stress that I don't question it either. What is the role of the Perfect Infinitive here? How would you rephrase this sentence?
I’d accept this sentence. “He’s had to be able …” would also work. I think this is a matter of style, but others might have a sifferent opinion on this.
How do you feel about: “He's had to have been able to have stayed alive”?
PS: If you, dear Moderators, think this question of mine would be better to have been written (Is it correct? Yes.
Or 'would have been better to have been written',
I wouldn’t write this.
since it IS already here) in a separate thread, then feel free to split this thread, and accept my deepest apologies,
Yes, it is. But you can still say. “It would be better to have been in a separate thread.” or “It would have been better in a separate thread.”
“It would have been better to send it to a separate thread”
“It would be better to have sent it to a different thread.”
There’s no need to double up on the past perfects in this case.
Please let me know if you still have doubts.

