Modals Express Attitude
Modal verbs don’t describe actions — they express how certain, obligatory, possible or advisable something is. They all follow the same grammar: modal + base verb, no -s, no to.
MUST — strong obligation/deduction
You must wear a seatbelt. (rule)
She must be tired. (logical deduction)
She must be tired. (logical deduction)
MUSTN’T — prohibition
You mustn’t smoke here. (forbidden)
SHOULD — advice/recommendation
You should see a doctor.
She shouldn’t eat so much sugar.
She shouldn’t eat so much sugar.
MIGHT / MAY — possibility (~50%)
It might rain later.
I may be late — not sure.
I may be late — not sure.
COULD — past ability / possibility
I could swim at age 5.
That could be the answer.
That could be the answer.
NEEDN’T — no obligation
You needn’t come. (it’s not necessary)
Must vs Have To vs Should
You must stop at red lights. (law — strong)
Rule/law — strong obligation
I have to work tomorrow. (external obligation)
Someone else requires it
You should drink more water. (advice)
Recommendation — not a rule
You mustn’t park here. (forbidden)
Prohibition — stronger than shouldn’t
You don’t have to come. (not necessary)
No obligation — free choice
💡 Memory Hack
The certainty scale
Line up modals from certain to uncertain: must (99% sure) → should (80% — advice) → may (50%) → might (40%) → could (30%). When making deductions, climb up the scale: “she could be sick” (possible) → “she might be sick” (more likely) → “she must be sick” (I’m almost certain).