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Or does it not refer to a perfect tense/aspect at all?
In any case, a modal perfect is neither a present perfect nor a past perfect.
The relationship of a modal to a modal perfect is somewhat like the relationship of a present tense to a past tense. The "have" of the modal perfect acts somewhat differently from the "have" of a true perfect tense.
The lights are still on in his office. He must be working late tonight.
The lights were still on in his office. He must have been working late that night.
I wonder what that loud sound is. Could/Might it be an airplane?
I wondered what that loud sound was. Could/Might it have been an airplane?
CalifJimCould is past tense of can. Why does your first example refer to the present? Is it only the past form with certain uses of 'could'?
Thank you again
English 1b3Could is past tense of can.In terms of its form, yes. But in terms of usage, note that the "past forms" of modals (would, could, should, might) are frequently borrowed into present (or future) time situations for various reasons, including politeness and uncertainty.
English 1b3Why does your first example refer to the present?Because I want to know now what the cause of the loud sound is. This is not a story about a loud sound I heard months ago. can or could or might in that type of question can be paraphrased as "Is it possible that (it is an airplane) ?".
English 1b3Is it only the past form with certain uses of 'could'?I think the discussion above has answered this question. Because of its spelling, it is always a so-called "past form", but with modals, as you've seen, the form is often a poor (or even misleading) clue to usage. So yes. In some grammatical patterns, could can function as an indicator of past time, but that doesn't mean that it always does so.
1) So this is an example of could being borrowed into the present due to it's being used to express uncertainty?
2) So if a modal is used as a past tense verb, then what happens if the perfect tense is then added to it?
past tense modal + perfect= ?
present tenese modal + perfect= past tense modal
English 1b3I wonder what that loud sound is. Could/Might it be an airplane?Yes. (Note that "borrowing into the present" is my own way of describing this. I doubt you'll find it explained that way in a formal textbook on grammar.)
English 1b32) So if a modal is used as a past tense verb, then what happens if the perfect tense is then added to it???? It changes meaning, depending on the verb. You would have to ask about specific cases with examples.
Your equations show that you believe there is actually some regular system of logic that underlies the use of modal verbs, and if only you could figure it out, you'd have the modals mastered! Believe me, it's too much of a mess to expect that! Each modal verb has its own pattern of usage, and no two are alike.
To master the modal verbs -- not easy -- requires understanding all the various situations in which each is used. Each occurs uniquely in certain patterns and not in others. There are "only" nine of them (18 if you count those with have separately), but each has some nasty surprises, as in negations, in interrogations, in if-clauses, when the speaker adds his feelings of uncertainty or politeness, or when they occur in older texts (100+ years ago) at a time when usage was different -- to name just a few of the problems.
I explain some of the most basic uses of some of the modals here: Modals. You might find it worth a read.
And here are a few more posts that might interest you. would, would have/ could , could have? could have been Could/would/might have done?t is this sentence correct? She could have done that ...
One more thing, and then I hope that I can solve most problems I have with modals on my own:
I often see passages in the present tense, which have one verb phrase (with a modal tense)expressing something that is about to happen (rather than something that is happening--as the present tense should do).
"I walk home and should find my mother sitting on the couch."
walk=present tense & present time
should find=??? Is this present tense& future time or present tense& present time?
"I wake up and walk out of my home. I can walk into the markets. I should find a place to buy a laptop."
can walk=how do we know whether this is (refers to??) present or future?
should find=same again...Is this present or future?
English 1b3expressing something that is about to happenModality is somewhat beyond tense and time; it's more like attitude. Your examples are not of things about to happen, anyway. They may happen; they may not happen.
can walk - have the [potential / ability] to walk. The potential is presently held by the speaker. Unless he loses that potential, he can use it at any time he chooses. This is present, whether or not the walking ever takes place.
should find (both cases) - expect to find. The expectation is presently held by the speaker. This is present, whether or not the finding ever occurs.
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