Must / Have To / Should

Three modals carry obligation and advice — and the difference is who decides. Must signals strong obligation from the speaker’s own view (I must send that email before I leave — it’s urgent). Have to signals external obligation: a rule, law, or schedule imposed from outside (She has to submit her timesheet by Friday). Should offers advice or recommendation (You should follow up with the client). The negatives diverge sharply: mustn’t = prohibition (forbidden); don’t have to = no obligation (not necessary); shouldn’t = advice against. That mustn’t / don’t have to distinction is one of the highest-stakes confusions at B1.

This worksheet drills B1 obligation and advice modals through workplace gap-fill and internal-vs-external choice tasks.

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Worksheet preview

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What’s inside:

• Grammar Box with all three modals, their negatives, and the speaker-vs-external decision criterion
• Gap-fill (10 items): choose between must, mustn’t, have to, don’t have to, should in workplace scenarios
• Must or have to? items with brief reason-writing — distinguish internal from external obligation
• Workplace email production: write three pieces of professional advice using should
• Full Answer Key plus Teacher Notes on the mustn’t / don’t have to divide

Common mistakes addressed: mustn’t meaning “don’t have to” (the German-speaker classic — You mustn’t come if you don’t want to), must to (with to), and should with an unnecessary to (You should to ask).

For: Adult and teenage learners (14+) at CEFR B1, in intermediate classes, 1:1 lessons, or self-study. Direct preparation for Cambridge B1 Preliminary (PET) and B2 First (FCE) — particularly the Writing tasks (advice emails, workplace rules, recommendations). Part of the Modal Verbs collection — the natural next step is Needn’t / Don’t Have To vs Mustn’t, which isolates the highest-stakes contrast practised here.