Could have, should have, would have

These past modal verbs are all used hypothetically, to talk about things that didn't really happen in the past.

Could have + past participle

1: Could have + past participle means that something was possible in the past, or you had the ability to do something in the past, but that you didn't do it. (See also modals of ability.) Couldn't have + past participle means that something wasn't possible in the past, even if you had wanted to do it. 2: We use could have + past participle when we want to make a guess about something that happened in the past. (See also modals of probability.) In this case, we don't know if what we're saying is true or not true. We're just talking about our opinion of what maybe happened.

Why is John late? We can also choose to use might have + past participle to mean the same thing: Should have + past participle

1: Should have + past participle can mean something that would have been a good idea, but that you didn't do it. It's like giving advice about the past when you say it to someone else, or regretting what you did or didn't do when you're talking about yourself.

Shouldn't have + past participle means that something wasn't a good idea, but you did it anyway. 2: We can also use should have + past participle to talk about something that, if everything is normal and okay, we think has already happened. But we're not certain that everything is fine, so we use 'should have' and not the present perfect or past simple. It's often used with 'by now'. We can also use this to talk about something that would have happened if everything was fine, but hasn't happened. Would have + past participle

1: Part of the third conditional. 2: Because 'would' (and will) can also be used to show if you want to do something or not (volition), we can also use would have + past participle to talk about something you wanted to do but didn't. This is very similar to the third conditional, but we don't need an 'if clause'. Try an exercise about these past modals here.

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'A' and 'The' Explained