A linguistics paper titled "Tense and Modals" by Tim Stowell shows these examples and explains them as follows:

(9) a. Carl can’t move his arm. (ability at the utterance time)
b. Carl couldn’t move his arm. (ability at a past time)
c. Max can’t go out after dark. (permission at the utterance time)
d. Max couldn’t go out after dark. (permission at a past time)

Example (9a) asserts that, at the utterance time, it is not possible for Carl to (habitually) move his arm. In (9b), could functions as a past-tense form of can in (9a); at some time prior to the utterance time, it was not possible for Carl to move his arm. Examples (9c-d) work similarly.

The last sentence in bold means:

In (9d), could functions as a past-tense form of can in (9c); at some time prior to the utterance time, Max was not allowed to go out after dark.

But can could really convey the meaning of permission at a past time?

In (9c), it is the speaker who doesn't allow Max to go out after dark. But in (9d), it can certainly be someone other than the speaker who didn't allow Max to go out after dark. And the speaker can be merely conveying his past inability to go out after dark. If this is the correct interpretation, can (9d) still be said to convey "permission at a past time"?

  • 4
    Not sure that "In (9c), it is the speaker who doesn't allow Max to go out after dark." 9d is ambiguous and probably relies on context to indicate whether it means ability or permission.
    – fev
    Oct 6, 2023 at 6:34
  • @fev Do you mean 9c is ambiguous?
    – JK2
    Oct 6, 2023 at 6:39
  • No, 9d. It can mean that Max was not able OR that he wasn't allowed. But I guess you could say the same about 9c, yes.
    – fev
    Oct 6, 2023 at 6:41
  • 1
    From CGEL : "Present tense 'can' is matched by 'could' in all the deontic and dynamic uses given in §9.3." Example given: " In those days we 'could' borrow as many books as we wished. [permission]"
    – user424874
    Oct 6, 2023 at 6:45
  • 1
    Exactly. It's categorically not the speaker's permission.
    – Andrew Leach
    Oct 6, 2023 at 7:53

3 Answers 3


"Could" is used also as a modal for conveying the idea of permission in the past.

CoGEL¹ § 4.52 can/could three major meanings of these modals can be distinguished.

(b) ABILITY […]
Can we borrow these books from the library?
• In those days only men could vote in elections.

In "(9c)" it is a matter of context whether Max has the permission to go out after dark. For instance, in "I know that Max can't go out after dark because his mother told me she wouldn't let him.", it is clearly Max's mother who does not allow it. The particular case to chose from "a" (possibility), "b" (ability) and "c" (permission) is dictated by the context.

¹ A Comprehensive Grammar Of The English Language

  • +1 for CoGEL quote! CoGEL says this: "For the 'ability' sense, can/could may be paraphrased by use of the be able to construction...It is possible to paraphrase can in the sense of permission by be allowed to: Are we allowed to borrow these books from the library?"
    – JK2
    Oct 6, 2023 at 7:46
  • 1
    If the question Can we borrow these books from the library? is directed to the librarian, it'd be more natural to paraphrase it as "Are we allowed to borrow...?" than "Are we able to borrow...?". But if it's directed to someone unrelated to the library, "Are we able to borrow...?" is also natural. Moreover, CoGEL says that you really can't replace could with might in In those days only men could vote in elections. If the deontic modality can readily denote past-time permission, why can't we use might for past-time permission?
    – JK2
    Oct 6, 2023 at 7:54
  • @JK2 It depends on context: if the question concerns books whose nature seems to be that of references, and if the person asking is not sure about this fact, then "be allowed to" is the more natural choice, as well as the proper one. However, if after some clarifications from the labrarian on a problem of availability of certain books, for instance as pertains to a peculiarly high frequence of borrowing, then "allowed to" is simply incorrect, and "able to + adverbial" is the proper choice ("Are we able to … at any time?"). (1/2)
    – LPH
    Oct 6, 2023 at 10:53
  • @JK2 It is usage that makes "might" a very unlikely choice for "permission in the past"; I see no other reason. It is a modal that has been restricted in its usage for permission: "may" has been restricted to the first person; "might" is not much used anymore for so called "tentative polite" asking of permission. It seems that this modal has been subjected to a certain atrophy or never was fully endowed with the expected possibilities; research is needed so as to determine which. (2/2)
    – LPH
    Oct 6, 2023 at 11:07
  • @JK2 I've certainly seen 'might' used deontically (subset permission), but it's rather old-fashioned. Examples: << may we one day wake up and find the state of Alabama, where all men might vote >> [prayer of Martin Luther King Jr] '' // << [I] voted for the equal suffrage of California women. I voted that women might vote because I knew ....>> [E S Stewart?; JSTOR] Non–vote-related examples are harder to find, as the usage is/was pretty formal. Religious usages ('that all might go in') tend to be indeterminate. Oct 6, 2023 at 11:24

It is the semantics that play a role here. The collocation go out after dark makes it more clear that it is about permission rather than having the ability to do so. The same explanation applies to both can and the past tense form could. However, there can be a context where can/could in "Max can/could go out after dark" would mean "is/was able to"; with the meaning having the capacity or time to do so.

OED lists the relevance sense of could as below and compares to might which was favored in the past. I'm also adding the earliest citation from 1539; and the last two citations from 1968 and 1996 of this usage of could from OED:

II.ii. The past tense could with temporal function.

II.ii.12. Expressing permission or sanction: was allowed to, was given permission to; = may v.1 II.iii.17.

For long regarded by grammarians as at best colloquial, and discouraged in favour of might.

1539 At that tyme no bysshop coulde be in Rome, without the ful consent & confyrmacyon of themperour.
J. Gough, translation of J. Le Maire, Abbreuyacyon Gen. Councellys sig. G.iiv

1968 Her mother insisted she could not go to the Halloween parade on an empty stomach.
B. Cleary, Ramona the Pest vi. 133

1996 Pierce, did you tell Bethany she could come with us?
T. Janowitz, By Shores of Gitchee Gumee (1998) 247

Oxford English Dictionary, s.v. “can, v.¹, sense II.ii.12”, September 2023.

Note: OED lists the same sense and the note for can also, comparing to may.

  • I don't have access to OED, so if there are any example sentences under the definition, could you show them in your answer?
    – JK2
    Oct 6, 2023 at 23:33

All modals have at least two meanings,

  1. the Deontic reading, which deals with social and behavioral norms, including giving and withholding permission, obligations, and taboos. Examples

    • You must be home by midnight.
    • She can go to the ball.
    • He should really call her.
    • If he will hand it in, it can be graded.
  2. the Epistemic reading, which deals with logic, (judgements of) probability, and expected (though not obligatory) behavior. Examples

    • This must be the place.
    • This can't be the place.
    • He should be home by now.
    • The 8:15 will actually leave at 11:30.

These are all hedged round with restrictions, irregularities, idioms, constructions, and exceptions; every modal has some, so there are no firm general rules.

For one instance, the epistemic sense of will (often called "the future tense", though it isn't) is not allowed in if-clauses, which means only the deontic sense (of 'be willing') occurs there.

  • *If it will rain tomorrow, we'll postpone it

For another, the epistemic sense of can is only allowed in negative environments; note that all the original examples given of can meaning "POSSIBILITY" are negative. Take out the negation and see what happens.

  1. Finally, can has not only a negative-polarity epistemic sense and a deontic sense of permission, but also a third sense, often called the Dynamic, which refers to ability, and shows up sometimes with past could:
  • When I was young, I could do 100 pushups; now I can only do 95.

"Permission at a past time" is somebody else's phrasing, and doesn't mean much. This is just ordinary ornery modal behavior.

  • 1
    What kind of modality's involved in these?: If it will cure the cancer, then the cost doesn't matter / If it will bring the rebels to the negotiating table, I am prepared to hand in my resignation etc? Oct 10, 2023 at 11:08
  • Something like effects of human actions forcing future expectations in hypotheticals. I'd say they weren't deontic. Oct 10, 2023 at 16:57

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