2

I think I could have failed this time as well.

Could the above phrase mean two things?

First it means that I could have failed without your help or something. So with help I could have been successful.

Second it means that I have a feeling that I failed. So there's still a chance of success and I'll have to wait a bit more.

Am I right?

2

Yes. As it stands, without context, the sentence is ambiguous. Which meaning it has depends on what time references are involved.

The ambiguity arises because of the dual use of the modal verbs can, may, will, shall.

All verbs may be used in past form with non-past reference, to express uncertainty. Ordinary verbs are only used this way in the if clause of conditional constructions:

If I had a computer I could send him an email.

Modal verbs, however, may also be used this way in ordinary declarative clauses. The consequence clause of the sentence above can stand on its own:

I could send him an email, but I won’t. ...

This is more or less equivalent to I can send him an email—it is merely a little more uncertain: It is possible, right now, for me to send him an email.

BUT!—what if you want to express a past possibility? Ordinarily, we ‘backshift’ a present-form verb into the past form to accomplish this:

I can send him an email today, and I will → I could send him an email yesterday, and I did.

But if your present expression employs a past form, you don’t have this option: you’ve already ‘used up’ your past form. The workaround is to use have + past participle as a ‘past marker’:

I could send him an email, but I won’t → I could have sent him an email yesterday, but I didn’t.

Consequently, there are two possible interpretations of could have failed. It may be a modal present perfect, representing a more uncertain version of can have failed

I could have failed, if I missed that last question. = It is possible, right now, that I have failed.

Or it may be a backshifted version of could fail:

I could fail, if you don’t help me. → I could have failed, if you hadn't helped me. = It was possible, then, that I would fail.


Note that can in this context has to be more or less equivalent to be possible rather than be able

  • As you explain, your last example (I could have failed, if you hadn't helped me.) could not be regarded as a subjunctive mood, right? ( "could" that I use here also means "be possible") @StoneyB – Kinzle B Mar 19 '14 at 4:32
  • @ZhanlongZheng ehh ... I get nervous when anybody uses the term subjunctive, because aside from be no English verb has any subjunctive forms, and I can never know what your teacher has used subjunctive to mean. – StoneyB Mar 19 '14 at 12:31
  • OK. We learnt grammar in Chinese at school. Before using this forum, I didn't know this "subjunctive" word. Anyway, "I could have failed, if you hadn't helped me." does not refer to a unreal condition as in "I would have failed, if you hadn't helped me." Am I right? @StoneyB – Kinzle B Mar 19 '14 at 12:41
  • @ZhanlongZheng Right. Could designates a possible outcome, not a certain outcome. Since you are speaking about the past, you probably know now whether you failed or not, so it's real or unreal now; but at the time it was merely possible. You might have succeeded even if he hadn't helped you. – StoneyB Mar 19 '14 at 12:48
  • I still feel a little confused. Let me put it this way. Still take your last two examples for instance, 1."I could have failed, if I missed that last question." means that it was likely that I missed it, but I am not sure whether I missed it or not. 2."I could have failed, if you hadn't helped me." means that you did help me, it is only a hypothetical for me to say "if you hadn't helped me." Is my explanation right? – Kinzle B Mar 19 '14 at 13:04

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