Introduction: Why Modals Matter

In the HKDSE, examiners aren't just looking for correct grammar; they are looking for nuance. Modal verbs are like a "volume knob" for your sentences. They tell the reader how sure you are about a statement. Whether you are identifying a writer’s tone in Paper 1 (Reading) or presenting an argument in Paper 2 (Writing), mastering degrees of certainty will help you sound more professional and precise.

Don't worry if this seems tricky at first! By the end of these notes, you will know exactly when to use must, might, or could to express your ideas perfectly.

1. The Certainty Scale: From 0% to 100%

To understand modal verbs, it helps to imagine a scale of probability. How sure are you that something is true?

High Certainty (90% – 100%)

Must: Used when you are almost certain something is true based on evidence.
Example: "The lights are off. They must be asleep."

Can't: Used when you are almost certain something is not true.
Example: "He just ate a huge meal. He can't be hungry already!"

Medium Certainty (50% – 70%)

Should / Ought to: Used when you expect something to happen because it is normal or planned.
Example: "The bus should be here in five minutes."

Low Certainty / Possibility (30% – 50%)

May / Might / Could: Used when something is possible, but you aren't sure. Might is often slightly "weaker" than may.
Example: "It might rain later, so bring an umbrella just in case."

Quick Tip: In HKDSE Paper 2 (Writing), using might or could instead of will makes your arguments sound more balanced and "academic." This is often called hedging.

2. Making Deductions: Present vs. Past

In the "Grammar in use" section, you need to know how to use modals to talk about the present and the past.

A. Certainty in the Present

The structure is simple: \( Modal + Verb (base form) \)

1. Must: "She has three trophies; she must be very talented."
2. Can't: "The door is locked from the inside; he can't be out."
3. May/Might/Could: "The shop is closed. They might be renovating."

B. Certainty in the Past

This is a common area where students lose marks. To talk about the past, we use a special formula:
\( Modal + have + Past Participle (V3) \).

1. Must have: You are sure something happened.
Example: "The ground is wet. It must have rained last night."

2. Can't have / Could not have: You are sure something didn't happen.
Example: "I saw him in Central at 2 PM. He can't have been in Mong Kok at the same time."

3. May have / Might have / Could have: It was possible, but you don't know for sure.
Example: "I can't find my keys. I might have left them at school."

Did you know? Could have can also be used to talk about something that was possible in the past, but did not actually happen.
Example: "You could have won the race if you hadn't tripped!" (But you didn't win).

3. Modals in the HKDSE Exam Context

Paper 1 (Reading)

Pay close attention to modals to identify the writer's attitude. If a writer uses "may" or "might," they are being cautious. If they use "must" or "will," they are being assertive and confident. Understanding this helps you answer questions about tone and mood.

Paper 2 (Writing)

When writing a Letter to the Editor or an Argumentative Essay, avoid saying "This will definitely solve the problem." Instead, use "This could help solve the problem." It shows you understand that social issues are complex.

Paper 4 (Speaking)

In Part A (Group Interaction), modals help you make suggestions politely.
Instead of: "We do this."
Try: "We could perhaps consider this option..."

4. Common Mistakes to Avoid

1. Using "mustn't" for deduction

Wrong: "He hasn't called. He mustn't have my number."
Correct: "He hasn't called. He can't have my number."
Explanation: "Mustn't" is for prohibition (things you are not allowed to do). Use can't or must not for negative certainty.

2. Forgetting the "have" in past forms

Wrong: "She must been tired yesterday."
Correct: "She must have been tired yesterday."
Explanation: Always use \( modal + have + V3 \) for past certainty.

3. Mixing up "Could" and "Can"

In the context of certainty, can is rarely used for specific possibilities. Use could, may, or might instead.
Wrong: "It can rain tomorrow."
Correct: "It could/might/may rain tomorrow."

Quick Review: Key Takeaways

1. High Certainty: Use must (positive) or can't (negative).
2. Low Certainty: Use may, might, or could.
3. Past Deduction: Use the formula \( Modal + have + V3 \).
4. Exam Strategy: Use modals to "soften" your claims in writing and to "read between the lines" in reading comprehension.

Memory Aid: If you are Mostly sure, use Must. If you Certainly doubt it, use Can't. If it's a Maybe, use Might!