Modals

A modal adds the speaker's attitude to a verb. Read the sentence and ask two questions: how certain is this, and how compulsory is this?

1. Ability and permission. can = ability or informal permission, could = past ability or a polite request, may = formal permission or possibility, might = a weaker possibility.
2. Obligation, graded. must = strong, from the speaker; have to = compulsion from outside (a rule, a timetable); should / ought to = advice; need not = no obligation at all; must not = prohibition. Those last two are opposites, not variants.
3. Deduction. must be = I am sure it is so; can't be = I am sure it is not; may be / might be = it is possible. "He must be at home; the light is on."
4. The past forms. modal + have + V3 carries regret or a guess about the past: "You should have informed us", "She must have missed the bus", "He could have passed."

A modal is always followed by the bare verb — no "to", no "-ing", no past form.

The single most common mistake among Marathi and Hindi speakers is stacking two obligations: "should have to", "must have to", "can able to". The Marathi पाहिजे / लागते constructions naturally pile up ("जावेच लागेल"), so the English copies them. How to spot it: a sentence may hold one modal only; if you see a modal followed by "have to" or "able to", delete the extra half.

modal + bare V1, never "to" · must = speaker's compulsion, have to = outside rule, should = advice · need not = no obligation, must not = prohibition (opposites) · must be / may be / can't be = certainty scale · regret about the past = should have + V3

Fill in the blank: "The examination has been postponed, so you ____ worry about the syllabus now." Options: must not / need not / cannot / should not. → need not. The exam being postponed removes the obligation to worry; it does not forbid worrying. Sanity check: "must not worry" would be an order not to worry, "cannot worry" would mean worrying is impossible, and neither matches the reason given in the first half of the sentence.