Consider the following two sentences:

  1. He can have cooked dinner (present)
  2. He could have cooked dinner (past)

I've been trying to understand how the "have cooked" part should be understood.

Is it in past tense relative to the "can" (present) and "could" (past), i.e. goes before/predates those times, or is it always relative to the present?

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    Cooked in both cases can be an adjective (formed from vpt), as in "fried chicken". However, in the second case, it can also be a vpt itself. Think again. – Kris Jan 6 at 15:49
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    "He can have cooked dinner" doesn't make sense on it's own. It could be part of a sentence such as "I don't see how he can have cooked dinner yet", meaning "I don't think it's possible that that the meal can be ready yet". – Kate Bunting Jan 6 at 16:51
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    Don't read 'have cooked'. Read 'could have' to mean it was possible to take place in the past. – Yosef Baskin Jan 6 at 17:07
  • Can have done something vs. Can have something done! Let us compare it with Future Perfect tense; He will have cooked dinner. Replacing WILL with CAN, it is He can have cooked dinner. That way, the usage refers to 'ability/ futurity' too. He could have cooked dinner, or He could have the dinner cooked, refers to something like 'undone past'. Hope I haven't confused. – Ram Pillai Jan 7 at 2:12
  • @YosefBaskin - is this true for both "can have cooked" and "could have cooked"? In both cases, we refer to something in the past relative to now (present)? – Shuzheng Jan 8 at 13:43

Of the two sentences given,

  • *He can have cooked dinner
  • He could have cooked dinner.

the first is ungrammatical. Epistemic can is a Negative Polarity Item, which means that it can only occur in a negative context, like this:

  • He can't have cooked dinner.

Without the negative in can't, though, it's ungrammatical.

So it's not "present" and "past". Can and could are two different modal auxiliary verbs, with different (though related) meanings, and quite different grammar requirements.

As to the second sentence, the have is the mark of the Perfect construction, which is always followed by a past participle of the next verb in the verb chain, as here by cooked.

The perfect construction is the only way to get a past time meaning (not "past tense") into a verb phrase that starts with a modal, because modals aren't tensed. Even though your textbook or teacher might tell you, they're talking about Middle English; Modern English modal auxiliary verbs are untensed. So you can't say, about the past:

  • *I musted go yesterday (you say I had to go yesterday instead)
  • *He coulded cook dinner (you say He could have cooked dinner)

How modals interact with perfect varies:

  • *can have is ungrammatical, but not could have
  • will have and would have are both fine but mean different things
  • *shall have is ungrammatical, but should have is fine
  • may have and might have are essentially identical in meaning.
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  • "He can't have cooked the dinner" may be negative polarity but it's definitely past in meaning, which should be pointed out to a learner. – Lambie Jan 30 at 23:54
  • True. It's an epistemic, so it means that it's impossible that he cooked the dinner (in the opinion of the speaker). – John Lawler Jan 30 at 23:57
  • I wonder if epistemic modality allows for 100% certainty. "He can't have done it." sounds pretty certain to me (90%-100%). "He didn't do it," is more of a statement of fact (also in the opinion of the speaker). But "he didn't do it" is not an epistemic, is it? (no modal verbs) – Eddie Kal Jan 30 at 23:59
  • This can't have translates to: It is not possible that he did it. It is certainty of "it is not possible that [verb in the past]". – Lambie Jan 31 at 0:03
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    As Robin Lakoff once pointed out, using any modal is less certain than simple assertion. He did it is much more certain than He must have done it; He didn't do it is more certain than He couldn't have done it. Use of the modal marks speaker's judgement rather than more objective certainty. – John Lawler Jan 31 at 0:34

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