Modal Auxiliaries (must, have to, should) | English Grammar Guide for French Students

• 1 Do not change form for different subjects (I must, you must, he must)
• 2 Do not use "to" before the main verb (must go, not "must to go")
• 3 Form questions by inversion (Must you? not "Do you must?")
• 4 Form negatives by adding "not" (must not, have to not)

1 Strong obligation: "You must complete the assignment" (personal authority)
2 Logical conclusion: "He must be tired after that long trip"
3 Prohibition: "You must not smoke here" (strong negative obligation)
4 Personal necessity: "I must call my parents"

• 1 "Students must wear uniforms" (school rule)
• 2 "You must be at least 18 to vote" (legal requirement)
• 3 "She must be at home" (logical deduction)
• 4 "You must not enter without permission" (prohibition)

1 External obligation: "I have to go to work" (external requirement)
2 Rules and regulations: "You have to show ID" (official rule)
3 Logical necessity: "We have to leave now" (circumstantial necessity)
4 Different tenses: "I had to", "I will have to", "I don't have to"

• 1 "I have to finish my homework before I can go out" (external obligation)
• 2 "You have to wear a seatbelt" (legal requirement)
• 3 "She has to wake up early" (work schedule)
• 4 "They had to cancel the trip" (past necessity)

1 Advice/recommendation: "You should see a doctor" (suggestion)
2 Expected situation: "He should be at home now" (expectation)
3 Regret about past: "You should have studied more" (past regret)
4 Moral obligation: "We should help others"

• 1 "You should eat more vegetables" (health advice)
• 2 "She should arrive soon" (expected arrival)
• 3 "You should have locked the door" (regret about past)
• 4 "We should respect others" (moral suggestion)

Modal	Strength	Source	Example
Must	Strong obligation	Internal/personal	"You must do this"
Have to	Strong obligation	External/authority	"You have to do this"
Should	Mild recommendation	Advice/suggestion	"You should do this"

1 Must have: Strong assumption about past: "He must have forgotten"
2 Had to: Past necessity: "I had to work late"
3 Should have: Regret about past: "You should have studied"
4 Won't have to: Future freedom from obligation: "You won't have to work tomorrow"

1 If clauses: "If you want to succeed, you must study"
2 With "would": "You should would call him" (mixed conditional)
3 With "ought to": Similar to "should" but more formal
4 With "need to": Less strong than "have to"

• 1 Using "must" for past obligations: "I must go yesterday" (incorrect) → "I had to go yesterday" (correct)
• 2 Confusing "must" and "have to" for source of obligation
• 3 Using "should" for strong obligations when "must" or "have to" is more appropriate
• 4 Forgetting that modals don't use "to" before main verbs

1 ✓ Correct: "You have to submit the report" (external requirement)
2 ✗ Incorrect: "You must submit the report" (when it's external)
3 ✓ Correct: "You should rest" (advice)
4 ✗ Incorrect: "You must rest" (unless absolutely necessary)

1. I _______ finish my homework before I can watch TV. (obligation)

2. You _______ see a doctor about that cough. (recommendation)

3. Students _______ wear uniforms to school. (school rule)

4. He _______ be at home now. (logical assumption)

5. We _______ leave early to avoid traffic. (external necessity)

6. You _______ have studied more for the exam. (regret)

7. They _______ arrive at 8 PM. (expectation)

8. Drivers _______ follow traffic laws. (legal obligation)

9. You _______ lock your door when leaving. (security advice)

10. I _______ call my parents tonight. (personal obligation)

1. have to

2. should

3. have to

4. must

5. have to

6. should have

7. should

8. have to

9. should

10. must

1 English: Uses modals (must, have to, should) with fixed structures
2 French: Uses conjugated verbs (devoir, falloir, pouvoir) with subject agreement
3 English: No subject agreement needed for modals
4 French: Requires agreement patterns for possessive and conjugation

• 1 English modals don't change for different subjects
• 2 "Must" = "devoir" (internal obligation), "falloir" (impersonal)
• 3 "Have to" = "devoir" (external obligation)
• 4 "Should" = "devoir" (recommendation) or "il faut"

1 Must: Think "I must do this myself" (internal/personal obligation)
2 Have to: Think "Someone made me have to do it" (external obligation)
3 Should: Think "I should probably do this" (recommendation)
4 Practice regularly: Use these modals in daily conversations

• 1 Create daily scenarios using each modal
• 2 Practice forming questions and negatives with each modal
• 3 Read English texts to see natural usage patterns
• 4 Focus on the strength of obligation for each modal

• 1 "Must" expresses strong personal obligation or logical conclusion
• 2 "Have to" expresses external obligation or requirement
• 3 "Should" expresses recommendation, advice, or expectation
• 4 Each modal has different strengths of obligation

Remember: Must = Strong personal obligation, Have to = External requirement, Should = Advice/recommendation

• Start with basic obligation expressions
• Gradually incorporate recommendations
• Focus on the context to choose the right modal