Granting permission with the potential form

Question

My previous question got me thinking about if/when the potential form or できる can be used to grant permission.　

My doubts come about because I'm pretty sure that using the potential form/できる is never correct when seeking permission. Please correct me if I'm wrong.

Consider:

写真を撮ることができるのは6時までです。
You can take photos until 6 o'clock.

Does this only represent the ability to take photos e.g "we do not allow access after 6 o'clock so photography is not possible", "it gets dark after 6 o'clock so you can't take pictures"? Or can it signify permission as well i.e. "We allow you to take photos only until 6 o'clock"?

There seems to be a grey area where the ability to do something is taken away because permission has been removed (like the allowing access example above), which I guess is the reason that 'can' serves both purposes in English.

Sundowner's statement in my previous question, "Regarding できる, it sounds natural when it is talking about the speaker allowing someone to take pictures, e.g. in case of a zoo.", suggests that できる can indeed be used to grant permission. I wonder in what circumstances this would be preferred to something like 撮ってもいいです.

Answer 1

In the context of seeking/granting permission, the potential form/できる can be used.

1. この美術館では写真を撮ることができます It is allowed to take pictures in this museum
2. ここでは飲食はできません Eating or drinking is prohibited here.
3. お借りできますか？ May I borrow this?
4. 試着できますか？ May I try it on? (for clothes)
5. サインもらえますか? Can I have your autograph?

For 1 and 2, I think てもいいです is hardly usable. Of course, you can casually say 写真を撮ってもいいです, but とってもかまいません or とっても大丈夫です would be usual for this particular sentence. For 3-5, you can use てもいいですか. Either sounds same to me though できますか may be more polite. (5 may not be exactly a permission.)

6. これ捨ててもいいですか？ Can I throw this way?
7. 入ってもいいですか？ May I come in?
8. お宅の子を写真にとってもいいですか Can I take a photo of your kid?

For 6-7, できますか is not usable (even choosing different verbs like 破棄する or 入室する). For 8 写真にとることはできますか sounds like asking a parent who is a complete stranger to the speaker (and probably is not with the child at the moment).

My tentative guess is that できますか is more neutral about the expected answer while てもいいですか usually expects yes. And there is some issues of register and collocation like 1-2/6-7 above.

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I'm not completely clear about difference of May I... and Can I..., but remember in a film an English learner's Can I come in? being corrected to May I come in? I have a feeling the difference above is somewhat comparable ...or maybe not.