1. I could play with my dear friends tomorrow at the seaside. Unfortunately, my sister happened to fall ill. I'll have to break my promise and stay at home to take care of her.

  2. I could play with my dear friends tomorrow at the seaside, but this all depends on whether my mom will allow me to.

I made up the two examples. Though it's not perfect, I just use them as tokens for my understanding. The idea around them is the key point here.

From my understanding, these two could are quite different:

Could in #1 is equivalent to "would be able to", meaning that I'm not likely to go to the seaside tomorrow. But I would be able to if my sister hadn't been ill. As PEU 124.7 indicates, could is used to express irrealis ideas.

Could in #2 is equivalent to "might", meaning that I'll probably go to the seaside if my mom allows me to. This is an example of the tentative usage of could.

PEU1 124.7 Could can be used to criticise people for not doing things.

You could ask before you borrow my car. (irrealis usage of could)

Could have + past participle is used for criticisms about the past.

You could have told me you were getting married.

Is my understanding right?

1. PEU = Michael Swan's, Practical English Usage.

  • 3
    I'm not convinced #1 is valid. Since the "playing" is irrealis in the past, it's no longer a possibility. So it should be "I could have played...". And had his sister not been ill, OP would have been able to play. Commented Jun 14, 2014 at 20:56
  • But the time is set in tomorrow. How could the "playing" be irrealis in the past? @FumbleFingers
    – Kinzle B
    Commented Jun 15, 2014 at 11:27
  • 1
    Because it became an unreal possibility in the past, when your sister fell ill and you realised that particular potential future was no longer an option. Commented Jun 15, 2014 at 12:25
  • In #1, can I say "I would play" or "I would have played" instead of "I could have played" with the intended meaning maintained? @FumbleFingers
    – Kinzle B
    Commented Jun 15, 2014 at 12:41
  • If it's would rather than could, you'd still normally use past tense ("I would have played [yesterday, now, tomorrow], but I broke my leg"). But it does become possible to use present tense, if you want to emphasis that at the time of speaking you're still willing to play (or would be willing, were it not for the fact that you've broken your leg). Commented Jun 15, 2014 at 13:05

1 Answer 1


Firstly, I'm not sure if the second clause in your first sentence is grammatical - you can't use unfortunately, but since but works as a conjunction between clauses, and unfortunately interrupts this.

Also: that first sentence makes more sense in the past tense:

I could have played with my friends, but ...

The only way I can imagine it making sense in the present tense is if it were being spoken aloud to oneself, as a train of thought.

  • could expresses ability, permissibility, or possibility.
  • may/might expresses possibility or permissibility.

In that regard, may can usually be replaced by could.

However, specific instances of could are defined by their co-text - in your case, what you've said is correct.

The first expresses (in)ability (though it's possibly also denoting permissibility or possibility, depending on whether you would consider it permissible or possible to go to the beach when your sister is ill, and whether or not you should be taking care of her).

It's not really criticism, since the the reason that "you/he could X" works is that it plays on a series of assumptions, for example:

"You could ask before borrowing my toothbrush!"

  1. I'm telling you that you could ask, which is an inane and fairly pointless observation on its own.
  2. Therefore, the assumption is that you don't ask, and
  3. I want you to ask.
  4. In this way, I'm criticising you for not asking.

The second expresses permissibility (but again, you could argue that it also expresses possibility, depending on whether you consider it a possibility that you would disobey your mother).

  • OALD gives an example: I shouldn't be too late. But it depends if the traffic's bad. I followed this pattern.
    – Kinzle B
    Commented Jun 14, 2014 at 16:42
  • What I was saying is that could in #1 is an irrealis usage of possibility while could in #2 is an real usage of possibility, but I'm not sure about it.
    – Kinzle B
    Commented Jun 14, 2014 at 16:54
  • @ZhanlongZheng both uses are irrealis moods - "go to the beach" is something that hasn't happened as you say it. In the first sentence, happened and have are real, and in the second, depends is, too.
    – jimsug
    Commented Jun 14, 2014 at 16:58
  • @jimsug The terminology is tricky around these questions. For some, irrealis embraces both counterfactual and tentative situations, for others it designates only counterfactual situations, and for yet others it designates the use of past forms with non-tense -basically, modal- significance. Commented Jun 14, 2014 at 17:55
  • Are both uses irrealis moods? I doubt that. Does that mean when could mean may, it is in fact that could is the irrealis form of "can"? @StoneyB
    – Kinzle B
    Commented Jun 15, 2014 at 8:15

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