‘You might ought to see the doctor.’ ‘It looks like it might could be.’ ‘You just figured they might could use another wolf or two.’ These lines from literature – by Janice Holt Giles in Shady Grove, Daniel Woodrell in Woe To Live On, and Cormac McCarthy in The Crossing – use a feature of grammar called a double modal, also known as a stacked modal or multiple modal.
Modal refers to modality or mood in grammar, which is not like mood in human feeling or physical atmosphere. Grammatical mood is about things that are possible, intended, permitted, obligatory, forbidden, wished for, and so on. Modal verbs allow us to turn She plays into She must play, She can’t play, She should play, She will play, and more. (Notice that modal verbs are not inflected: He may arrive, not *He mays arrive.)
Can, could, will, would, shall, should, may, might, must, ought, and dare are modal verbs (aka modal auxiliaries, or just modals for short). Combine them and you get a double modal. The most common forms, at least in American English, are might could, might can, and might would, but many other pairs occur: might should, may can, should ought, must can, may will, and so on. Different combinations will be more or less typical or acceptable for different users.
Negative types occur too, such as this one in Joe Lansdale’s novel Captains Outrageous: ‘you could actually go some places you might not go, might not could afford to go.’ And then there are triple modals, like: ‘I might will can go tomorrow.’ This line appears in the excellent database MultiMo, short for multiple modal, a less common but more accurate term, since sometimes more than two modals are used (as with double negative and multiple negation).
Double modals are not part of standard English, which allows only one modal at a time. Unless they’re part of your dialect (they’re not in mine), you won’t see or hear them often. In the US, they’re especially common in southern states but are attested ‘across a wide geographical area’, according to the Yale Grammatical Diversity Project.
Double modals also occur in northern English and Scots dialects. You can hear might can in an audio clip at the recently launched Scots Syntax Atlas. The researchers found evidence of various types of double modal in Scotland, such as will can, would can, used to can, and used to could, as well as question types: Could you might get here early?
You might ought to listen out for them.