过去情态动词
英语 B2 知识点 7 4:07 英语旁白 · 英中内嵌字幕
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Modals talk about the present: it might rain. To talk about the past, English adds have plus the participle. The memory hook: the modal is a detective, and have plus participle is its time machine. Must have deduces: he must have missed the bus; he's not here, and the evidence is clear. Can't have rejects: he can't have left already; the lights are on. Might have shrugs: he might have forgotten; he does that. And should have blames: you should have called me; you didn't; we waited.
The deduction scale. Must have: I'm sure it happened; she must have studied, the test was perfect. May, might or could have: possibly; he might have forgotten, he does that. Can't have: it surely didn't happen; they can't have left already, the lights are on. The key collision: the opposite of must have is can't have, never mustn't have; mustn't forbids, can't have deduces. And could have does double duty: possibility, or unused ability — I could have won; the talent was there, the trophy wasn't.
Pause and choose. You can't have smoked here; the ashtray is clean, so the detective rejects the smoking. Mustn't have mixes a rule with a deduction, shouldn't have blames you for smoking you didn't do, and the fourth option is a grammar smoothie with too many ingredients.
Should have plus the participle is the blame tense. Should have: the right thing didn't happen; you should have studied, and the test noticed. Shouldn't have: the wrong thing did; you shouldn't have eaten my noodles, and I noticed. Ni benlai yinggai fuxi de is exactly this: the unlived correct past. It is how friends express disappointment and how teachers mark essays, and both are permanent records.
Pause and choose. I must have called her: the phone bill proves it, so the detective deduces. Should have would blame me for not calling, which is the opposite of the bill's testimony. Don't send the detective to do the scolding.
The forms are one calm chain: modal plus have plus participle, every person, no changes. I must have, she must have, they must have. Questions flip the modal: could he have forgotten? Negatives: can't have, shouldn't have, might not have. And the pronunciation trap: have compresses to a soft uhv, should've, could've, would've, which is why people write should of. It is never of. The detective weeps.
Pause and choose. You should have called. In writing, have in full; in speech, should've. Should of tells the reader you learned English by ear alone, and should had sends the wrong verb form into the chain. Modal, have, participle: the three links hold or the deduction falls.
Play detective with the classroom evidence. The teacher is smiling: she must have read our essays. Or she can't have read them yet; both are possible, one is hopeful. He can't have finished the homework; the ink is still wet from the shop where he bought the pen. I should have slept earlier; I shouldn't have watched that last episode; the episode was worth it, and the detective disagrees.
Pause for four checks. He must have missed the bus: the detective is sure. They can't have left already: the detective rejects. You should have called: the blame tense. And I could have won: unused ability; the talent was there, the trophy wasn't. Next topic: relative clauses, now with commas — the defining and the non-defining.