Anglais • 1ère

Expressing Obligation, Ability and Possibility
The Verbal Group - Modal Auxiliaries and Semi-modals

Expressions Overview
📝 Expressing Obligation, Ability and Possibility
Using modal auxiliaries effectively
OBLIGATION
✅ must do
✅ have to
✅ should do
📝 must study
ABILITY
✅ can do
✅ could do
✅ be able to
📝 can swim
🎯
Definition: Modal auxiliaries express different degrees of obligation, ability, and possibility.
📚
Obligation: Must (strongest), have to (external), should (advice).
🔄
Ability: Can (present), could (past), be able to (alternative).
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Possibility: May, might, could (varying degrees of likelihood).
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Tip: Use "must" for speaker's strong opinion, "have to" for external rules
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Attention: "Could" can express past ability or polite request
⚡
Rule: Modals are followed by base form of verbs (no "to")
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Method: Practice with real-life situations for each expression type
OBLIGATION
must: strong requirement
have to: external rule
should: advice
ABILITY
can: present ability
could: past ability
be able to: alternative
POSSIBILITY
may: possible
might: less likely
could: possible
PROHIBITION
mustn't: forbidden
can't: not allowed
shouldn't: not advisable
Obligation Exercises
1 Expressing Obligation
Instructions :

Choose the appropriate modal to express different types of obligation.

Step 1: "Students ___ wear uniforms" (have to)

External rule imposed by school → Use "have to"

Complete: "Students have to wear uniforms"

Step 2: "You ___ study hard for the exam" (must)

Speaker's strong opinion → Use "must"

Complete: "You must study hard for the exam"

Step 3: "You ___ drink more water" (should)

Advice/recommendation → Use "should"

Complete: "You should drink more water"

Step 4: "Drivers ___ stop at red lights" (must)

Legal requirement → Use "must"

Complete: "Drivers must stop at red lights"

Step 5: "Children ___ be home by 9 PM" (have to)

Parental rule → Use "have to"

Complete: "Children have to be home by 9 PM"

Answers :

1. have to, 2. must, 3. should, 4. must, 5. have to

Obligation Rules :

• Must: Speaker's strong opinion or logical deduction

• Have to: External requirement/rule

• Should: Advice or recommendation

2 Expressing Ability
Instructions :

Complete the ability expressions with appropriate modals.

Step 1: "When I was younger, I ___ run very fast" (could)

Past ability → Use "could"

Complete: "When I was younger, I could run very fast"

Step 2: "She ___ speak four languages fluently" (can)

Present ability → Use "can"

Complete: "She can speak four languages fluently"

Step 3: "If I had more time, I ___ learn guitar" (could)

Conditional ability → Use "could"

Complete: "If I had more time, I could learn guitar"

Step 4: "He ___ not lift heavy objects after his injury" (can't)

Present inability → Use "can't"

Complete: "He can't lift heavy objects after his injury"

Step 5: "I ___ swim across the river when I was 10" (could)

Past ability → Use "could"

Complete: "I could swim across the river when I was 10"

Answers :

1. could, 2. can, 3. could, 4. can't, 5. could

Ability Rules :

• Can: Present ability

• Could: Past ability or conditional ability

• Can't/Couldn't: Inability

3 Expressing Possibility
Instructions :

Complete the possibility expressions with appropriate modals.

Step 1: "It ___ rain later today" (might)

Uncertain future possibility → Use "might"

Complete: "It might rain later today"

Step 2: "She ___ be at the party tonight" (may)

Present possibility → Use "may"

Complete: "She may be at the party tonight"

Step 3: "The package ___ arrive tomorrow" (could)

Possible situation → Use "could"

Complete: "The package could arrive tomorrow"

Step 4: "He ___ have forgotten the appointment" (might)

Past possibility → Use "might have"

Complete: "He might have forgotten the appointment"

Step 5: "You ___ not want to go there alone" (might)

Uncertain advice → Use "might"

Complete: "You might not want to go there alone"

Answers :

1. might, 2. may, 3. could, 4. might, 5. might

Possibility Rules :

• May: Permission or possibility

• Might: Less likely possibility

• Could: Possible situation

Advanced Expression Exercises
4 Mixed Expressions
Instructions :

Identify and use the correct expression type in mixed contexts.

Step 1: "Students ___ submit their assignments on time" (must/have to)

Academic requirement → Could be either depending on context

Complete: "Students must/should submit their assignments on time"

Step 2: "___ you help me with this problem?" (could)

Polite request → Use "could"

Complete: "Could you help me with this problem?"

Step 3: "She ___ speak Chinese and Japanese" (can)

Present ability → Use "can"

Complete: "She can speak Chinese and Japanese"

Step 4: "It ___ be sunny tomorrow" (might)

Weather prediction → Use "might"

Complete: "It might be sunny tomorrow"

Step 5: "You ___ not smoke in this building" (mustn't)

Prohibition → Use "mustn't"

Complete: "You mustn't smoke in this building"

Answers :

1. must/have to, 2. Could, 3. can, 4. might, 5. mustn't

Mixed Expression Rules :

• Context Matters: Consider the speaker's intention

• Politeness: Could/Would for polite requests

• Prohibition: Mustn't/Can't for negative obligations

5 Modal Perfect Constructions
Instructions :

Complete the modal perfect constructions for past situations.

Step 1: "She ___ have studied harder for the exam" (should)

Past regret → Use "should have"

Complete: "She should have studied harder for the exam"

Step 2: "You ___ have told me earlier" (could)

Past possibility → Use "could have"

Complete: "You could have told me earlier"

Step 3: "He ___ have passed the test" (must)

Past logical deduction → Use "must have"

Complete: "He must have passed the test"

Step 4: "They ___ have arrived by now" (should)

Past expectation → Use "should have"

Complete: "They should have arrived by now"

Step 5: "We ___ have prepared better for the meeting" (ought to)

Past obligation → Use "ought to have"

Complete: "We ought to have prepared better for the meeting"

Answers :

1. should, 2. could, 3. must, 4. should, 5. ought to

Modal Perfect Rules :

• Should have: Past regret or expected completion

• Could have: Past possibility

• Must have: Past logical deduction

Key Points Summary
🎯
Modal Rule: All modals are followed by base form of verbs (no "to")
🔍
Obligation Levels: Must > Have to > Should (strongest to weakest)
⚡
Politeness: Could/Would are more polite than Can/Will
📋
Prohibition: Mustn't (forbidden) vs Can't (not able to)
Obligation
must, have to
should
Ability
can, could
be able to
Possibility
may, might
could
Expressing obligation, ability and possibility Modal Auxiliaries and Semi-modals