Point 69 in the category of MODALITY: DEDUCTIONS AND CONCLUSIONS: ‘must’ to guess and deduce, most commonly with ‘it must be’, or ‘you must be’. *We cannot ensure automatically that this form will point to the usage. We have deleted some ngrams that are obviously not the usage. Both examples in the EGP are followed …
Modality is the grammatical expression of the speaker’s attitude or opinion about the possibility, necessity, or certainty of an action or state. Can’t is a modal verb that shows the negation of the verb can. It means that the subject is unable to do something, such as perform an action or demonstrate an ability. It can also be used to express deduction, which is a logical inference based on evidence or reasoning. For example:
She can’t swim. (ability)
He can’t be at home. It’s too early. (deduction)
In the English Grammar Profile, B2 point 137 in MODALITY is defined as: negative forms of ‘can’t’ and ‘cannot’ to guess, predict and deduce. This point is an extremely difficult point to locate because it heavily relies on usage. The use of ‘can’t’ is A1 by default, but not ‘cannot’ which has not been given …
