I ask about the possibility of can. I would like to ask further to the past Stack Exchange answer.


What is the difference between 'can', 'could', 'may' and 'might'?

The following sentence is part of the answer to the question.

Furthermore, modern English, the semantics of can stretches to cover that of may (but only in the area of permission, rather than possibility).

I respect this answer. then, modern English, why didn't the semantics of can stretch to cover that of may in the area of possibility?

A: It may be that the bird escaped from the cage last night.

B: * It can be that the bird escaped from the cage last night.

(This example sentence is taken from Sawada Harumi(1991: 208).)

  • But it can. Maybe. Right? :)
    – Lawrence
    Jan 19, 2023 at 6:49
  • It can get cold at night where I live. That's a distinct possibility, whether or not I give permission (same as It may get cold). I think perhaps the distinction you're making only arises when it may be is connected to a that- clause. Jan 19, 2023 at 14:30

3 Answers 3


The answer to this question, and the question quoted in this question, is the same, really.

Put as an aphorism, it's simple enough:

  • Every Modal Auxiliary Verb In English Is Unique.

Every one of the 9 auxiliary verbs has some partial resemblance and partial parallelism to other modals -- but none of them are completely parallel, all participate in different idioms, all have different meanings when combined with negations and quantifications, none of them are paradigmatic in any useful way. Each one is unique, in other words.

Modal auxiliary verbs are basically on the road to becoming new inflections, the way the verb forms of Latin habere became the paradigmatic person markers of Romance future tenses. They've been stripped of all their inflections (except the -d/-t in the 5 modals formed from preterite roots, which adds a syllable in negative contractions), so their paradigms are no longer available (thou mayst or thou mayeth?), and their monosyllabic structure slips through the contractions to show up as a consonant here and a nasalization there in ordinary speech.

Can is a good example of just how weird (another word for unique, really) modal auxiliaries can be. First, there are several categories for modals.

  • A modal auxiliary is either a Necessary modal, like must, or a Possible modal, like may. Necessary modals include must, shall, will, should, would, and Possible modals include can, could, may, might. Necessary is also called "Square" and "Possible" is also called "Diamond", because of the logical symbols used for them. Every language has both types of modal, though they aren't always auxiliary verbs as in English.

  • A modal auxiliary verb can contract, and usually does, with other auxiliary verbs, negative morphemes, prepositions, complementizers, and other components of the verb phrase. This can get quite complicated. In some American dialects, affirmative can is pronounced with a higher lax vowel /kɛn/, instead of /kæn/. The negative can't, however, is pronounced /kæn/, with the final /t/ suppressed. Or the /kn/ sequence (especially with a syllabic /n/) might get used by itself:

    • /ˌknɛnibəɾi'siyəm/ Can anybody see him?
  • Every modal auxiliary has at least two senses, with various names, of which the two most common are the Deontic, or "Social" sense, like the deontic must of

    • Cinderella must be home by midnight.
      Deontic senses have to do with authority, permission, obligation, and control of behavior. They often stem from social prohibitions and prejudices, rather than logic or planning.

    and the Epistemic, or "Logical" sense, like the epistemic must of

    • Cinderella must have gone to the wrong party
      Epistemic senses represent conclusions affirmed by the speaker, generally after consideration of circumstances, times, past behavior, and motives, of what seems to be most or least likely situation.

Note that can does not normally use an epistemic sense in the affirmative:

  • *This can be the right place

does not mean

  • This might be the right place.

It means, if anything, that if enough work were done to transform it, that it could be made into the right place, rather than that there is a possibility we've arrived.

Provided it's in a negative environment, however, we can (deontic) use an epistemic can, because epistemic can is a Negative Polarity Item.

  • This can't be the right place.

Can has another sense beside its epistemic and deontic senses, however; it has to do with personal ability. Indeed, be able to is the usual periphrastic equivalent of ability can

  • He can/is able to leap tall buildings at a single bound.

This doesn't mean he just did it, or does it often, or in fact has ever been seen to do it -- just that he has the capacity, according to the speaker. This entails the possibility, of course, but it's a different sort of possibility.

And that's what one finds every time when investigating modals -- they're sui generis to a fault. Every single one has dozens of special functions and constructions and interpretations that are welded or glued or stapled or soldered into or onto or underneath some part of the Big Machine, and they all work. More or less. But there really aren't many useful generalizations except the one I put in boldface above.

  • Oh, one more weirdity of can but no other modal: with sense verbs (see, hear, feel, smell, taste and the verb idiom speak (a language), use of can is equivalent to simple present tense: I can speak Spanish/hear the band/smell the peanuts == I speak Spanish/hear the band/smell the peanuts Jan 19, 2023 at 18:50
  • This looks like a real goldmine! I'll probably end up revisiting it repeatedly over the coming days / weeks / years. But I'm intrigued by on the road to becoming new inflections. I have the impression English is very different to, say, Latin, largely because English has "evolved" to use word order and "function" words to do the job of Latin inflections. But if modals can turn into inflections, that feels like something different is going on. Compared to other languages today, does English make significantly more (or less) use of modal verbs? Jan 19, 2023 at 18:50
  • Modals are all over the place. Every time I started investigating something, there'd be weird modal constructions to cope with. Essentially, they've been released from their verbal duties and are seeping in here and there wherever they can be made to fit in. It'll be a while before they settle down. Jan 19, 2023 at 18:52
  • I think politicians love modals, because they make it so much easier to says things in a way that requires active engagement from the audience to "choose" the intended meaning. Trump is often accused of not having great command of English, but I think he's a past master at writing tweets that his supporters interpret favourably, but which enrage his detractors (he's not interested in communicating with his political enemies; he just likes winding them up! :) Jan 19, 2023 at 18:59
  • +1 for your thoroughness. You are quite learned. Are you claiming that 'He can still be alive' is not a counterexample to the claim that negative polarity obtains to epistemic 'can'? The property of aliveness is not a capacity or ability, but an essential property. I'll reread to see if I misstepped.
    – J D
    Jan 19, 2023 at 19:25

Can does stretch to cover the "possibility" sense of may, but it uses could.

It could be that the bird escaped last night.

It's part of a conditional construction, which I'm going to leave to others' answers to flesh out.


A: It may be that the bird escaped from the cage last night.
B: * It can be that the bird escaped from the cage last night.

Can absolutely expresses possibility. There's nothing wrong with B, but it does have a slightly different meaning. Merriam-Webster's definition of 'can' is evidence that can is used for possibility. In fact, the example is modal-adverb-copula:

—used to indicate possibility
Do you think he can still be alive? Those things can happen.

Anyone who tells you that can can't be used to describe possibility is completely ignorant of modal logic and the basics of modality. The real question is what sort of possibility is expressed? 'Can' expresses factual possibility and one of its subjunctive cousins 'could' expresses hypothetical possibility. The difference between 'can' and subjunctives is one of what philosophers of language call propositional attitude. One can view the difference between factuals versus hypotheticals and counterfactuals as expressing a degree of confidence in belief. So, your two sentences might be translated for clarity:

A: It may be that the bird escaped from the cage last night.

I'm not sure that the bird escaped from the cage last night. It might have happened.

B: It can be that the bird escaped from the cage last night.

It is possible that the bird escaped last night. Birds escape cages.

PS On rereading my post, I've done the same thing as a hedge in one of my final sentences:

your two sentences might be translated for clarity

I could have written 'your two sentences can be translated for clarity', but I did not. Why? Because philosophically, translation is a sticky business with issues of indeterminacy, and having many arguments about synonymy and translation, it was prudent of me to offer that my reasoning is opening to defeat. :D

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