Modal verbs can be used to indicate ability, permission, possibility, necessity, etc. Unfortunately, not all modal verbs can be used in any types of tenses in English, so we need to know their alternative forms as well.
We can’t say “I must go to the hospital yesterday”. We can’t use “must” in simple past form; therefore, we need to change the modal verb “must” with “had to” – the simple past form of “have to”.
INCORRECT: I must go to the hospital yesterday.
CORRECT : I had to go to the hospital yesterday.
For negation, we don’t need to add a helping verb.
• Julie need not worry about money. Her father is a wealthy man.
• She must not go out alone at night.
need not = do not have to
must not = be not allowed to
If we want to indicate a situation in the past, we have to use the alternative forms instead of the regular modal verbs.
• Julie didn’t have to worry about money. Her father was a wealthy man.
• She wasn’t allowed to go out alone at night.
Now try this exercise: Fill in the gaps. Use the correct substitutes of modals.
Graham _____ (cannot) go skiing since his accident.
Graham hasn’t been able to go skiing since his accident.
1. Last year my brother _____ (must) learn a lot of new words.
2. I _____ (cannot) go to Tina’s party last weekend – my parents said “No!”
3. Next year I _____ (must) learn more in Latin because I want to get better marks.
4. I hope my parents _____ (can) buy a new car next year.
5. You _____ (needn’t) answer all the questions in the test yesterday.
Leave your answers in the comment, and I’ll check up on your work later.