Coursebooks often introduce must, have to, and should together as "modal verbs of obligation," which invites students to treat them as synonyms with different levels of politeness. They're not — the difference is about where the obligation comes from, and teaching that distinction explicitly prevents years of vague, interchangeable use.
1. Start with should for advice — the lowest-stakes modal
"Should" gives an opinion or piece of advice, with no real obligation attached — "You should drink more water." It's the safest starting point because there's no rule to get wrong, only an opinion to form. Practice it with everyday problems (a friend is tired, a classmate is stressed about an exam) and have students respond only with "should/shouldn't," building fluency before any obligation modal enters the picture.
2. Teach must vs. have to as internal vs. external obligation, not formal vs. informal
This is the distinction most materials get vague about. "Must" is used when the obligation comes from the speaker's own judgment ("I must call my mother, I haven't spoken to her in weeks"). "Have to" is used when the obligation comes from an outside rule or authority ("I have to wear a uniform at school"). Give students a sorting exercise with real classroom/life rules (external → have to) against personal resolutions (internal → must) so the distinction is felt, not memorized as a formality label.
3. Isolate mustn't vs. don't have to as its own drill — they are opposites, not synonyms
This is the single most tested and most confused pair in the whole topic. "You mustn't smoke here" means it's prohibited — don't do it. "You don't have to bring lunch" means it's optional — no obligation either way. Students who understand must/have to individually often still get this pair backwards, because "not obligatory" and "prohibited" feel like they should be near-synonyms in negative form. Drill it as a matched pair every time: mustn't = forbidden, don't have to = optional.
Common mistakes and how to catch them
- Mustn't/don't have to reversed: "You don't have to smoke here" meant as a prohibition. Fix with the matched-pair drill above, every time it comes up, not just once.
- Must/have to used as free variants: "I must wear a uniform" (should be "have to," it's a school rule, not personal judgment). Always ask "whose rule is this?" before choosing.
- Adding "to" after must: "I must to go now." — students copy the "have to" pattern onto "must," which never takes "to." Drill must + base verb as a fixed chunk.
A 45-minute lesson shape that works
- 5 min — Warm-up: elicit advice for a common problem using "should," no writing yet.
- 10 min — Present must vs. have to with the internal/external sorting exercise using real rules and resolutions.
- 10 min — Controlled practice: choose must or have to for 8-10 sentences, justifying the choice out loud.
- 10 min — Isolated drill: mustn't vs. don't have to matched pairs, 6-8 items, correcting reversals immediately.
- 10 min — Freer practice: students write the rules of their house or workplace using must/mustn't/have to/don't have to.
Free worksheets for this lesson
These printable PDFs follow the same progression above — should first, then must/have to, with the mustn't/don't have to contrast built in:
- Should / Shouldn't – Grammar Focus (A2) — advice modal, the safest starting point.
- Should / Shouldn't – Reading: Health and School Problems (A2) — receptive practice giving advice in context.
- Should / Shouldn't – Writing: Give Advice (A2) — freer production giving advice for real situations.
- Must / Have To – Rules & Obligations Grammar (A2) — internal vs. external obligation, with the mustn't/don't have to contrast.
- School & Public Rules – Must / Have To Reading (A2) — receptive practice with real rule-based texts.
- Must / Have To – Write Rules for a Place (1) (A2) — freer production writing rules for a place of the student's choice.
- Modal Verbs of Obligation and Necessity – Grammar (B1) — extends the topic with more nuance once must/have to is solid.
Once obligation modals are secure, the same modal family extends naturally into Modal Verbs of Possibility (might/could, B1) and Modal Verbs of Deduction (must/can't be, B1) — worth a follow-up lesson rather than adding them here.
Browse the full set of grammar worksheets or filter by A2 level.