X should have Y to Z (in the past)

Question

I was doing some literature homework today, when I became confused as to whether or not the following sentence is grammatical:

X and Y should have killed Z to have prevented Z from killing them.

Should "to" be swapped out for "in order to", or is the whole sentence just plain wrong?

Answer 1

The sentence as it stands calls for a simple infinitive, not a perfect infinitive:

X and Y should have killed Z to prevent Z from killing them.

For a perfect infinitive to be appropriate, it would have to be something on the order of:

X and Y would have had to have killed Z to have prevented Z from killing them.

Answer 2

It would mean the same thing. In order to can usually be reduced to just to, and in order not to can often be substituted with to or in order to, followed by an antonym for the subsequent verb.

As for whether the whole thing is "just plain wrong" see other posts regarding verb tenses.

Answer 3

There's nothing at all incorrect in the example sentence X and Y should have killed Z to have prevented Z from killing them. It simply means that X and Y are now dead because Z killed them. Had they killed Z, he would not have been able to kill them and they would not now be dead. If that's not the case, then the sentence is semantically incorrect but grammatically correct.

I disagree with StoneyB about this, but his substitute sentence is perfectly fine, just one of those unreal conditionals that can also be expressed as "If X and Y had killed Z [but they didn't = unreal past condition], that would have prevented Z from killing X and Y". The sentence you ask about is not a conditional but a judgment about what should have been done to prevent the killing of X and Y.

There's no difference between saying "You should have listened to my advice not to buy Apple stock to have prevented (your) losing $10,000 overnight" and "You would have had to have listened to my advice not to buy Apple stock to have prevented (your) losing $10,000 overnight".