Should/would+perfect infinitive or modals could, might+perfect infinitive and the perfective future aspect [closed]

Solution 1:

I have modified the original question, stripping irrelevancies following comments, to:

Can constructions like

• (If you gave it to me in December,) I would have finished the task already by January

with or without the if-clause, mean that the action in the main clause is slated to be finished by the defined time in the future?

One reason why it's hard to answer this question is because the vocabulary is strange. One pulls a task off only if the task is a crime, usually involving theft, for instance. And slated to refers to a particular official slate of events, which is contrary to the presuppositions of pull the task off. Who's keeping the slate, and how are they related to the task? And then already refers to some previous completion estimate and its incorrectness. The original mentioned giving instruments, and that's even more problematical.

Judging grammaticality requires imagining a context in which the sentence makes sense, and then judging how difficult that was. In this case, there are so many incongruities in the example sentence. I've taken quite a few liberties with it already, but I think the question is about what the speaker expects the listener to assume about what the speaker expected to happen, as contrasted with what really happened. And maybe what some schedule listed as supposed to have happened.

A sentence I can imagine a native speaker tumbling against constructions comprising of mixed modals and perfects might use (i.e, might speak aloud with an intention to communicate with someone who's attending to them) is

• I would have finished the task by January.

This means that my estimate is, or was, January. The difference in tense depends on what actually is meant. This could be counterfactual: You didn't get it to me in time and I didn't finish it, though if you had I (think I) would have.

Or it could be simply hypothetical estimating: You want it done by January; all right. If you can manage to get it to me in time, I (estimate I) would have it finished by January.