It is said that can and may both are used as a sense of possibility.

If that’s the case, then what is the difference between:

  • It can be very dangerous to cycle at night.

  • It may be very dangerous to cycle at night.

  • 2
    Not much difference between those two; either could be used in almost any circumstances with the same sense. But all modal verbs have several senses and peculiar syntax, and the usages of can and may are very different. Commented Aug 1, 2015 at 19:03
  • In that context there is very little difference. In other contexts the difference between can and may is quite significant.
    – Hot Licks
    Commented Aug 1, 2015 at 20:41
  • "Can I eat the last cookie?" "Yes you can." (It's physically possible to eat it.) "May I eat the last cookie?" "No you may not." (You'll ruin your supper.)
    – Hot Licks
    Commented Aug 1, 2015 at 20:43
  • In addition, might or could seem to work equally well. Frustrating, isn't it, when you've been taught that each of these is different! Commented Aug 2, 2015 at 12:02

3 Answers 3


It can be very dangerous to cycle in the night.

This indicates that there are certain circumstances that make it dangerous, e.g.

It can be very dangerous to cycle in the night, for example: if you are cycling without any lights, if you are cycling through a rough area, if you are cycling after a night at the pub.

It may be very dangerous to cycle in the night.

This indicates uncertainty.

It may be very dangerous to cycle in the night but I'm not sure - it may be perfectly safe.

  • if 'can' is used then does it mean that it is 100% dangerous to cycle in the city ?
    – iamRR
    Commented Aug 1, 2015 at 19:20
  • @iamRR - It's dangerous to get out of bed in the morning.
    – Hot Licks
    Commented Aug 1, 2015 at 20:22
  • I would compare it to "It can't be true"/"it may not be true" or "He can be sarcastic"/"He may be sarcastic".
    – Centaurus
    Commented Aug 1, 2015 at 20:47
  • 1
    @iamRR - No, it means that it's dangerous under those particular circumstances. They might not always apply. Commented Aug 1, 2015 at 22:16
  • @chaslyfromUK -- And what are those particular circumstances ?
    – iamRR
    Commented Aug 2, 2015 at 4:26

Most English speakers do not pay attention to the the subtleties between these words and treat them like synonyms. In this context, I believe it is more appropriate than some others, since they can both just mean possibly in their own ways. Can is a little more indirect in that meaning, whereas may is more direct but imprecise because it can also note permission. However if you want to read deeply enough into it there might be some arcane distinction.


Probable understanding: It is able to be dangerous. This ability does not have to be exercised, indicating it might not be dangerous but it is nevertheless possible.

Unlikely implication: It might optionally imply the night is known to haves the means establish to be dangerous, such as its own darkness, which makes it hard to operate your bicycle safely.


Probable understanding: It might be dangerous in the sense of there is a chance it is, rather than strength. It is possible but not ascertained.

Unlikely implication: Using this instead of can might indicates you do not know if there are circumstances which could make it dangerous, like thugs or nocturnal monsters taking cover under darkness are actually there. It might be dangerous, if circumstances permit it to be.

Sometimes we might use what is considered the past tense of can, could, when discussing hypothetical ability similar to how we might use would as a hypothetical will. In this case, it seems as if either is appropriate. "I would go, if I could." demonstrates future tense use of both words.

If the author wanted to signify that riding the bicycle at night is certainly dangerous, what probably should have have been written is "It is very dangerous to cycle in the night". There would be no need to modify the substantive verb, noting the existence of danger, with an auxiliary verb and doing so may actually be detrimental to comprehensibility

Definitions of can, may, could, would, is, substantive and auxiliary which are used as external reference material are all found in the Hallen, Cynthia, ed. Renovated Online Edition of Noah Webster’s 1844 American Dictionary of the English Language, http://edl.byu.edu/index.php .


There is no difference. From the OED

Can [B. II. With infinitive, as auxiliary of predication] 5. Expressing a possible contingency; = May

  • Lovely. Another drive-by downvote. I would be happy to express your reservations to www.oed.com if I only knew what they were.
    – deadrat
    Commented Aug 1, 2015 at 21:14
  • 1
    I didn't vote against the answer myself but since you seem befuddled I'll posit a hopefully helpful hypothesis: You did not contrast the referenced definition of may, against a definition of can to actually demonstrate the perceived differences or more accurately in this case, the lack of a difference.
    – Tonepoet
    Commented Aug 1, 2015 at 21:59
  • @Tonepoet I am not befuddled, because there is nothing in a drive-by downvote to be confused about. There's nothing. Which is why DBDVs are a curse upon this forum. Thank you for your hypothesis, which made me realize that I had omitted the head word "can,"which" I have supplied. I needed to make explicit what was only implied, namely that this is a definition of "can" as a synonym of "may." Do you, yourself find a need for more contrast, or is this a need you impute to others?
    – deadrat
    Commented Aug 1, 2015 at 23:35
  • Now with the fix, the answer seems fine to me since it is a self-contained analysis of both words in the sense that applies from a respectable source. There's only so much you can do to contrast the same shade of grey. I guess my hypothesis was wrong though, since this was voted against again. I'm not entirely sure why this received another nay vote.
    – Tonepoet
    Commented Aug 2, 2015 at 0:37
  • 2
    My answer might be more speculative but Noah Webster's A.D.E.L. is a citable source, isn't it? I just didn't want to quote it verbatim this time. Anyway I think what he takes issue with is the word possibly based upon that but in analyzing this definition I personally take that to mean that to mean, is that while the words share this one sense, they differ in other contexts. Maybe an explanation as to why this sense applies over the others might be useful in that regard .
    – Tonepoet
    Commented Aug 2, 2015 at 4:21

Not the answer you're looking for? Browse other questions tagged or ask your own question.