Obligation
Which modal verb expresses a strong obligation originating from the speaker?
Must
Which verb expresses almost 100% confidence in the present? (He ______ be at home — the lights are on)
Must
Which verb expresses the ability in the present?
Can
Does the form of the modal verb change by person (I / he /she)?
No (He can, She must — without-s)
She musts go to school every day.
She musts go to school every day.
Which verb is typically used when the obligation comes from an external source (rules, law, schedule)?
Have to
Which verb expresses the weakest possibility?
Might
How to tell about the ability in the past?
What comes after the modal verb?
Infinitive without to (I must/need/must)
I can to play the guitar very well.
I can to play the guitar very well.
The difference: “I must go now” vs “I have to go now”. Which expresses a personal decision more strongly?
must (speaker's personal commitment)
The difference between may and might is in assumptions.
might — slightly less likely than may
What is the difference between can and could when expressing an ability?
can — ability in the present
could — ability in the past (or a polite/less confident form)
Is it possible to add suffixes to modal verbs (-ed, -ing, -s)?
No. Modal verbs do not change.
He mights be tired after the long trip.
He might be tired after the long trip.
How do I say “I don't need" (no need)?
don’t have to / needn’t
How to express the negative deduction: “He can't be at home” (almost 100%)?
can’t / couldn’t be at home
Why does the sentence “I could swim across the river yesterday” sound unnatural to most native speakers, and how to replace it correctly?
Because could usually expresses a general ability in the past, rather than a specific successful outcome in a particular situation.
Correct options:
• I was able to swim across the river yesterday
• I managed to swim across the river yesterday
How to form a question with a modal verb correctly, and what is the main difference from regular verbs (such as do/does/did)?
The modal verb is placed before the subject, the auxiliary verb do/does/did is not needed.
He must to finish the report by Friday, otherwise the manager will be angry.
He must finish the report by Friday, otherwise the manager will be angry.
Why can't you say “I must to go"?
After MUST, the infinitive goes without to
Is it possible to use must to make assumptions about the past? What's the right thing to do?
Da. it must be V3 (He must have left)
Is it possible to say “I can to speak English"? Why?
No. After can, the infinitive without to
How to correctly form negation with must, can and may, and why can't you use don't /doesn't/ didn't? What is the important semantic difference between mustn't and don't have to?
Negation is formed directly with the modal verb:
• mustn't (prohibition)
• can't / cannot
• may not
The auxiliary do/does/did is not used because modal verbs themselves act as an auxiliary.
She can’t has left the office already — her computer is still on and her bag is here.
She can’t has left the office already — her computer is still on and her bag is here.
For deduction about the past, can't/must + have + V3 is used)