- Choose the right modal of deduction according to how certain you are, in the present and in the past.
- Express blame and regret with should / shouldn't have + past participle.
- Recognise the five characteristics of persuasive writing and apply them in a 180–200-word essay.
🌳 Concept tree
Unit 3→Modal Verbs of Deduction and Persuasive Writing
├── Present deduction
- │ ├── must / may / could / might / can't + base verb
│ └── Degrees of certainty
├── Past deduction
- │ ├── must have / may have / might have / can't have + past participle
│ └── Evidence-based guessing
├── Blame and regret
│ └── should / shouldn't have + past participle
├── Persuasive writing
│ ├── Five characteristics
│ └── Language of persuasion
└── Practice with full answer key
Degrees of certainty
| Modal |
Certainty |
Example |
| must + base verb |
95–100% sure it is true |
They must be tired after walking all day in the heat. |
| may / could + base verb |
about 50% possibility |
The waves may be stronger than before. |
| might + base verb |
about 30% possibility |
The fishermen might need to change their methods. |
| can't + base verb |
95–100% sure it is NOT true |
- This can't be the right place
- the map shows we are far away
|
- Positive evidence that makes you almost certain → must.
- Evidence against the idea → can't, not mustn't. Mustn't means prohibition, not deduction.
- A possibility you cannot confirm → may / could / might; might is weaker than may in exam keys.
- Sentences from the unit "The risks can't be completely avoided, but they can be reduced." / "Families should take precautions during storms."
- She … be at home; her lights are off. → can't
- They … be tired after walking all day in the heat. → must
- This … be the right place; the map shows we're still far away. → can't
Degrees of certainty in the past
| Modal |
Meaning |
Example |
| must have + past participle |
we are near certain it happened |
The streets are flooded. There must have been a heavy storm last night. |
| may have + past participle |
we are uncertain it happened |
She may have forgotten about the meeting. |
| might have + past participle |
we are very uncertain it happened |
They might have heard the announcement. |
| can't have + past participle |
we are certain it did NOT happen |
They can't have heard the announcement — they didn't show up. |
modal + have + past participle (V3)must have experienced, can't have caused, might have felt.
Never use the past simple after a modalmust have went is wrong.
- The streets are flooded. There … been a heavy storm last night. → must have
- They … heard the announcement — they didn't show up. → can't have
- She … forgotten about the meeting. It's likely. → may / might have
The two forms
should + base verb→ advice about the present or the future: You should eat more vegetables.
should have + past participle→ blame or regret about the past: You should have taken an umbrella.
shouldn't have + past participle→ criticism of a past action: You shouldn't have left the windows open.
- Fishermen should have prepared earlier for the changes in the sea.
- Citizens should have listened carefully to awareness campaigns in the past.
- The state should have invested in sea walls many years ago.
- You look tired. You … (go) to bed earlier. → should go
- We … (help) him when he asked for support. → should have helped
- It was raining. You … (take) an umbrella. → should have taken
- She … (listen) to her teacher more carefully. → should have listened
- You … (eat) more vegetables. They're good for you. → should eat
The five characteristics
| Comparison aspect | Main idea | Example | Keywords |
|---|
| Clear opinion or point of view | the writer states their position clearly | — | writerstatespositionclearly |
| Strong reasons and evidence | - reasons
- facts
- examples or statistics support the opinion
| — | factsexamplesstatisticssupport |
| Emotional appeal | - words that make the reader feel something — fear
- hope
- guilt or pride
| — | wordsmakereaderfeel |
| Persuasive language | - must
- should
- need to
- important
- urgent
- we all know
- clearly
- obviously
- and rhetorical questions
| "What will happen if we do nothing?" | mustshouldneedimportant |
| Call to action | tells the reader what to do after reading | — | tellsreaderwhatafter |
| Comparison aspect | Main idea | Example | Keywords |
|---|
| Problem | worldwide issues | - climate change
- poverty and hunger seem impossible for one person to affect
| worldwideissuesclimatechange |
| Claim | - these problems can't be ignored and require collective action
- small but meaningful steps combine into a huge impact
| — | theseproblemsignoredrequire |
| Call to action | - reduce waste
- support ethical businesses
- advocate for fair policies — and recognise that every positive action contributes to a larger solution
| — | reducewastesupportethical |
| Function |
Useful language |
| Stating the claim |
It is clear that… · I firmly believe that… · The truth is that… |
| Adding force |
must · need to · urgent · obviously · we all know |
| Emotional appeal |
Imagine a city where… · What will happen if we do nothing? |
| Call to action |
Start today by… · It is time for each of us to… |
- Write a persuasive essay of 180–200 words on "Small Actions, Big Impact".
- Keep one claim, two reasons with evidence, one emotional appeal, and a final call to action.
A. Complete with a modal of deduction
- Many people in poor regions … (not cause) climate change, but they suffer the most. → can't have caused
- That community … (experience) serious flooding after last week's hurricane. → must have experienced
- Activists … (feel) frustrated when leaders ignore their demands. → may / might feel
- You haven't eaten anything since morning, you … be hungry. a. must b. might c. can't d. should → a
- It's very cold outside, but the windows are open. He … have forgotten to close them. a. must b. should c. can't d. shouldn't → a
- The alarm didn't go off last night, so it … have been turned off by mistake. I'm sure. a. must b. might c. can't d. should → a
- There is no food in the fridge. She … have gone shopping this morning. a. must b. might c. can't d. may → b
- The garden looks wet. It … have rained last night. a. must b. might c. can't d. should → a
- He … be at home now because his car is not in the driveway. a. must b. might c. can't d. should → c
- They … left early because their bags are gone. a. must have b. might have c. can't have d. should have → a
- The lights are still on even though everyone left. Someone … forgotten to switch them off. a. must have b. might have c. can't have d. should have → a
C. Listening task: Climate Change and Coastal Cities
- Why are coastal cities like Alexandria at risk? What do scientists emphasise about sea levels? What problems do families and shop owners face? How can the state protect coastal areas? What can citizens do to help?
- Answer these from the audio track before you look at any transcript — the exam tests detail, not memory of the topic.
💡 High-yield traps
- mustn't is prohibition; for negative deduction about the present use can't.
- can't have + V3 means certain it did not happen; must have + V3 means certain it did happen — never swap them.
- After a modal, always the base verb (present) or have + V3 (past), never a past tense form.
- should have looks back with regret; should looks forward with advice. The time reference in the sentence decides.
- In persuasive writing, a strong opinion without evidence scores low; every claim needs a reason.
- Do not confuse persuasive (convince the reader to act) with argumentative (win a debate with a counter-argument).
