PE-51: Modal Verbs: The Full Strength Scale
Every modal on one page, arranged by strength — obligation, certainty and ability — plus how each one moves into the past.
PE-51: Modal Verbs: The Full Strength Scale
You have met every modal verb English has. Now, just as PE-41 did for the tenses, this lesson puts them all on one page. The secret is that modals are not a random list — they line up on scales of strength, and choosing the right one is simply choosing how strong you want to sound. Keep this lesson open when you write.
In this lesson you will learn
- The three families: obligation, certainty, ability
- Every modal arranged from strongest to weakest
- How each one moves into the past
- The four rules that govern all of them
1. Scale one: obligation and advice
| Strength | Modal | Meaning | Example |
|---|---|---|---|
| 100% | must / have to | obligation | You must wear a helmet. |
| 80% | had better | advice + warning | You'd better hurry. |
| 70% | should / ought to | advice | You should rest. |
| 30% | could / might | suggestion | You could ask him. |
| 0% | don't have to | not necessary | You don't have to come. |
| ✗ | mustn't / can't | forbidden | You mustn't smoke. |
Remember the crucial point from PE-45: the bottom two rows are not the same. Don't have to frees you; mustn't forbids you.
You must wear a seatbelt (the law). You'd better wear a coat (it's freezing). You should wear something smart (my opinion). You don't have to wear a tie (it's up to you).
Xavfsizlik kamarini taqishingiz shart. Palto kiyganingiz maʼqul — juda sovuq. Chiroyliroq kiyinsangiz yaxshi boʻlardi. Galstuk taqishingiz esa shart emas.
One topic, four strengths — that is the whole scale in action.
2. Scale two: certainty
| Certainty | Present | Past |
|---|---|---|
| 100% — I know | He is at home. | He was at home. |
| 95% — almost sure | He must be at home. | He must have been at home. |
| 70% — I expect | He should be at home. | He should have been at home. |
| 50% — perhaps | He might / may / could be. | He might have been. |
| 5% — almost sure not | He can't be at home. | He can't have been at home. |
The light is on, so she must be in. Her car has gone, so she can't be here. She might be at her sister's.
Chiroq yoniq, demak u uyda boʻlsa kerak. Mashinasi yoʻq, demak bu yerda boʻlishi mumkin emas. Opasinikida boʻlishi mumkin.
3. Scale three: ability and permission
1Ability now
can — I can swim.
2Ability in the past
could (general) · was able to (one success)
3Other times
be able to — will be able to, have been able to
4Permission
can → could → may (increasingly polite)
4. Moving into the past
Modals have no past tense of their own. Each one solves the problem differently:
| Present | Past | Example |
|---|---|---|
| can (ability) | could / was able to | I could swim at five. |
| must (obligation) | had to | I had to leave early. |
| mustn't (forbidden) | wasn't allowed to | We weren't allowed to talk. |
| must be (deduction) | must have + V3 | She must have forgotten. |
| should (advice) | should have + V3 | You should have told me. |
| will | would | He said he would come. |
I can swim now. I couldn't swim as a child. Last summer I was able to swim across the lake. Next year I'll be able to teach my little brother.
Hozir suza olaman. Bolaligimda suza olmasdim. Oʻtgan yozda koʻlni suzib oʻta oldim. Kelasi yil ukamga oʻrgata olaman.
One ability, four times — and only be able to can reach the future.
5. The four rules, one last time
- No -s: she must, he can, it should.
- No "to" after them — except ought to and have to.
- Questions by inversion: Can you…? Should I…? Must we…?
- Negatives with "not": can't, mustn't, shouldn't, won't — never don't.
6. Common mistakes
You don't have to smoke here — it's forbidden.
You mustn't smoke here.
He mustn't be at home — his car is gone.
He can't be at home.
Yesterday I must go to the doctor.
Yesterday I had to go to the doctor.
I should of called you.
I should have called you.
Next year I will can drive.
Next year I will be able to drive.
Practice
1 Choose: You ? touch that wire — it's live!
Show answer
mustn't (or can't) — this is prohibition, not free choice.
don't have to would mean it's optional.
2 Put into the past: She must be very tired.
Show answer
She must have been very tired.
Deduction moves into the past with have + V3, not with had to.
3 Order by strength: should · could · must · had better
Show answer
must → had better → should → could. From obligation down to a gentle suggestion.
4 Which meaning of must? (a) You must be Afsona's brother. (b) You must finish by six.
Show answer
(a) deduction — I'm guessing who you are. (b) obligation — I'm telling you what to do.
5 Fill in with any suitable modal: I ___ swim when I was six, but I ___ dive — I was too afraid.
Show answer
could … couldn't. General past ability, positive and negative.
Key words — Kalit soʻzlar
- Modal verbmodal feʼl
- Strengthkuch darajasi
- Obligationmajburiyat
- Certaintyishonchlilik
- Deductiontaxmin, xulosa
- Prohibitiontaqiq
- Permissionruxsat
- Helmetdubulgʻa
- Wiresim
- To divesho'ngʻimoq
🎯 Remember this
- Modals are scales, not lists — choose by how strong you want to sound.
- Obligation: must → had better → should → could → don't have to.
- Certainty: must be → should be → might be → can't be.
- In the past they change word: had to, could, must have + V3, should have + V3.
- The four rules: no -s, no to, invert for questions, not for negatives.