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X can be Z

X may be Z

Can these two expressions be used interchangeably, or is there a subtle difference? If so, could you explain it?

I have been checking many usage examples and they seem 100% interchangeable. I have found many instances of exactly the same sentence using both can and may, and, to me, their meaning seems to be the same.

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  • I hate examples with X, Y and Z on English websites UNLESS they are showing patterns of speech. In real life, sentences with X, Y and Z are meaningless. Please provide proper examples with "may" and "can" that you consider interchangeable.
    – Mari-Lou A
    Feb 13, 2023 at 16:04
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    Compare "We can park here" and "We may park here". Is (are) the meaning(s) identical? And "Ice can change into water" with "Ice may change into water“ Are we speaking about permission, ability or possibility?
    – Mari-Lou A
    Feb 13, 2023 at 16:05
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    @FumbleFingers It is worth noting that the accepted answer to that question is rather incomplete. (See my answer below.)
    – alphabet
    Feb 14, 2023 at 6:11
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    @alphabet: Point taken. Imho, ideally it would be better if this question had been closed, and your (excellent) answer was there on the question I linked to (hoovering up votes into the infinite future! :) But mods very rarely "merge" questions like this, even though in this specific case the actual question is so "non-specific" no-one could possibly claim it's somehow subtly different to the earlier one, so I guesss we are where we are. Unless this question and/or your answer get huge numbers of upvotes, in which case I might eventually vote to close that one in favour of this one! Feb 14, 2023 at 11:30

5 Answers 5

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This depends heavily on context. In many cases they are indeed the same. In other cases, though, they mean different things.

For one example, consider these two sentences:

  1. I can walk ten miles, but I definitely won't.
  2. I may walk ten miles, but I definitely won't.

Sentence 1 is perfectly fine: it means you're capable of walking ten miles, but you would never choose to do so.

Sentence 2 is nonsensical: it means that your walking ten miles is both a genuine possibility and a thing that will never happen.

Edit: if you want an example with "can be," here's a similar pair of sentences:

  1. He isn't a manager, but he can be one.
  2. He isn't a manager, but he may be one.

Again, sentence 1 is fine, but sentence 2 does not make sense.

In other words: "can" often expresses ability. "May" in this context only expresses possibility.

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  • When used to describe possibility, both "can" and "may" can refer either to epistemic possibility (certainty) or ontic possibility (chance); English doesn't generally make a sharp distinction between the two.
    – alphabet
    Feb 14, 2023 at 17:05
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"May" carries the sense of permission, of courtesy, and of uncertainty, depending on context.

"Can" carries the sense of ability, possibility, and potential, depending on context.

Examples:

"I can swim." (I am able to swim.)
"I may swim." (I haven't decided yet if I will or not.)

"I may get good grades." (I'm not sure yet, but there's a chance of this.)
"I can get good grades." (I know it's possible--perhaps I have done so before.)

"He can be nice." (He is known to be nice sometimes.)
"He may be nice." (It is uncertain whether or not he will be nice.)

"It can rain at any time in the jungle." (Rain is always a possibility.)
"It may rain today." (There is an uncertain chance of rain.)

Note: It would be grammatically incorrect to say "It can rain today" if one meant to say there was a chance of rain. Saying "It could rain today" would be more correct. "It can rain today" would mean that the speaker is willing to have the rain, perhaps is prepared for it (and may or may not have been ready for rain earlier), and is nearly a challenging statement, inviting the rain.

Grammatically, the words "can" and "may" are almost always interchangeable; but the meaning will change as well.

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To me, "may" is inclined more towards probability and "can" is inclined towards possibility. So if you say "x may be y" it's closer (but not completely identical to) "x is probably y".

The meaning will not be lost in either sense and you will be understood perfectly well when speaking whichever you choose, but that is the subtle difference to me as a native speaker.

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X can be Z = possible

X may be Z = possible + likely

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X can Y = "X is able to do Y."

X may Y = "X will do Y if given permission/allowed by something/someone."

  • It is possible that the "something/someone" giving permission is X itself, in which case the meaning is more like "X will do Y if X wants to."

  • The above doesn't work with questions. You can't ask "May you X?" to mean "Do you want to X?", the meaning will always be "Are you allowed to X by someone else?"

It can rain = It is able to rain.

It may rain = It will rain if it wants to.

Can rain be something that "wants?" Not scientifically, but figuratively. Both sentences arrive an effective inexact meaning of "there is a possibility of rain" which is typically good enough unless you are a meterologist.

There is also a phenomenon with English modals that they are often "misused" to convey politeness or respect. If your boss asks "May John use your computer?" they are not really asking for permission, they are just being polite.