modal auxiliary verb
Definition - An auxiliary verb that expresses possibility, probability, desire, and constraint, e.g. can, may, might, could, must, ought.

Yossarian the Grammarian on modals and auxiliaries.

Note that he uses "I have a goiter" as an example. Nice.

Example -
He might go home.

Etymology -
The term derives from the Latin modus, measure or manner or mode

Oxford English Dictionary -
Its first citation is from 1933:
"The modal auxiliaries may, might, can, could, must, ought, … give a cast to the whole sentence in which they are.
(E. H. Grout Stand. Eng. v. 122)

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