According to Practical English Usage by Michael Swan, modal auxiliary verbs do not normally have past tenses:

The modal auxiliary verbs are will, would, shall, should, can, could, ought, may, might, and must. Their grammar is different from that of other verbs: for example, they have no infinitives, participles or past tenses [...] Modal verbs do not have infinitives or participles (to may, maying, mayed do not exist), and they do not normally have past forms.

So can each modal auxiliary verb be considered to be in the present tense (in form, not meaning)? Since the modal auxiliary verbs are finite and they do not have past tense forms (according to Michael Swan's Practical English Usage), each must be in a present tense form.

Or are will, can, may and shall the present tenses (in form, not meaning) and would, could, might and should the past tenses (in form, not meaning)?

What about the modal auxiliary must?

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    Does "Practical English Usage" only have one sentence saying something like "modal auxiliary verbs do not normally have past tenses", or does Swan give more explanation of what he means by that? I think it would depend on what you mean by "past tense".
    – herisson
    Dec 24, 2017 at 23:51
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    @sumelic The following is a quote from Michael Swan's Practical English Usage: "The modal auxiliary verbs are will, would, shall, should, can, could, ought, may, might and must. Their grammar is different from that of other verbs: for example, they have no infinitives, participles or past tenses...Modal verbs do not have infinitives or participles (to may, maying, mayed do not exist), and they do not normally have past forms".
    – user217372
    Dec 25, 2017 at 10:33
  • @sumelic By "past tense", I mean the form of the modal verb. I'm not talking about the meaning.
    – user217372
    Dec 25, 2017 at 11:02
  • But toucans exist. Image from animals.sandiegozoo.org/sites/default/files/2016-11/…. ;-)
    – Jim
    Dec 25, 2017 at 15:53
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    This essentially comes down to how you prefer to describe the language. Some would say that can and could are two completely unrelated modal verbs in Modern English which both have only one form; others would say that they are the morphological present- and past-tense forms of the same verb, which happens not to have any other morphological forms than those two. There are arguments for and against both views. There is no final, authoritative answer on this. Dec 25, 2017 at 16:01

2 Answers 2


Getting back to the original question (asked 3 years, 8 months ago by someone who's left the group since), the actual answer is that whether you should consider modal auxiliary verbs to be inflected for tense depends entirely on what your grammatical system's definition of "inflected for tense" is, and how your grammatical system uses tense inflection.

For instance, some grammars of English insist that every sentence have a main tensed clause. Since modal auxiliaries can occur in simple sentences, these would have to be assigned a tense (typically Present, by default) by that grammar. On the other hand, your grammar might simply except modals from that requirement, or it might not have that rule at all, using something else instead.

No modern grammar that I know of distinguishes the historical present and past forms of modals (may, can, shall, will vs might, could, should, would, must) in any useful way, so the various final -t's and -d's are merely etymological curiosities, like the a-'s in awake, atop, aloft, and asleep.

A semantic past-present difference shows up with can/could in the ability sense, and will/would in the deontic 'willing to' sense. Both past descriptions refer to repeated behavior:

  • When I was young, I could do 100 pull ups; now I can only do 99.
  • When he was young, he would talk by the hour; now he won't say a word.

But that's about it; there's no tense or meaning difference between He might do it and He may do it -- both are possible, and that's it. Should has a special meaning as a weak must, both deontic and epistemic:

  • She should/must go to the ball. (weak/strong obligation to go)
  • This should/must be the place they mentioned. (weak/strong likelihood)

and, in the US at least, shall is not used for the future like epistemic will, but rather is restricted to two very special and limited deontic question constructions:

  1. First person singular question - an offer to do a favor for the addressee

    • Shall I open the window?
  2. First person plural question - an invitation to do something with the addressee

    • Shall we dance?

And, as you note, there is no historic present tense for must, as there is in German, where modal auxiliary verbs are not defective verbs like English modals, but real strong verbs, with all their principal parts, inflected regularly for everything.

So, if your grammar (and every linguist creates their own grammar of their own language) requires English modals to have tense, Voila! they do. If not, not. If you prefer, some may have tense and others may not. Questions like this are not matters of fact; they're arbitrary, so you might as well take whatever answer you like. It's your grammar, after all.

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    “…your grammar might simply except modals from that requirement.” perhaps exempt?
    – Mari-Lou A
    Sep 11, 2021 at 18:13
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    Exempt would work; but except is the verb we get exception from. Sep 11, 2021 at 20:46

Modals have neither a past tense nor a present participle. Let's take the example of "can", in the sentence, "I can play the piano." The past tense of can doesn't exist; there is no such word as "can-ed". To express the intention of "I 'can-ed' play the piano", you must paraphrase: "I have been able to play the piano." Similar workarounds are required for "may" ("I was allowed to play the piano.") The lack of a present participle for modals poses the same problem, and requires the same tactic of paraphrase: "Can-ing play the piano makes me very happy" becomes "Being able to play the piano makes me very happy."

"Must" has no past tense. "Must-ed you have missed your son's ball game?" is expressed by, "Did you have to miss your son's ball game?".

There was a time when the Germanic origins of American English indeed regarded "could", "might", "should", and "would" as past tense forms of modals, but no longer (except for some uses of "could" as the past tense of "can"). SEE, http://www.ling.upenn.edu/~beatrice/syntax-textbook/box-modals.html

  • 4
    What about "I could play the piano", for example in the sentence "Sally knew that I could play the piano" (which looks like a past-tense equivalent of "Sally knows that I can play the piano")? Is that what you mean by "some uses of 'could' "? Why doesn't it ever apply to "might" and "would"?
    – herisson
    Dec 25, 2017 at 4:14
  • Yes, that is how I would interpret the guidance regarding can/could. "Might" is the past tense of "may", but not in the sense of being permitted to do something. "I may stay up until midnight" could imply that the speaker is contemplating staying up that long, or that the speaker's mother has given permission to the speaker to stay up that late. In the first case "might" can certainly be used instead of "may", but it still means that the speaker is still considering how late to stay up, and does not render the sentence a statement of an action in the past.
    – Allen S.
    Dec 25, 2017 at 4:36
  • In the second example, "might" substituting for "may" entirely distorts the meaning, destroying the sense of permission granted by someone other than the speaker. It does not connote that the permission to stay up until midnight was granted in the past.
    – Allen S.
    Dec 25, 2017 at 4:39
  • I'm sure the extrapolation of the reasoning using "may" and "might" will explain why "would" does not operate as a past tense of a "could" as an auxiliary modal.
    – Allen S.
    Dec 25, 2017 at 4:42
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    The can/could ‘exception’ (if indeed an exception it is) is parallelled in will/would: “She knows that I will be there” vs “She knew that I would be there”. Dec 25, 2017 at 15:56

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