Modals of Deduction & Speculation (C1/C2)
📌 Lesson contents
🎯 Lesson goal (C1/C2)
Modals of Deduction are used to say how sure we are about a fact, based on logical clues or evidence. Unlike modals of obligation, here modals become tools for “reasoning”. Mastering them means telling apart exactly a logical certainty, a logical impossibility and a remote possibility. 🚀
🌟 Deduction about the Present
We use these modals when we make deductions about a situation happening now:
| Modal | Degree of certainty | Example |
|---|---|---|
| Must | Almost total certainty (logic) | You look pale; you must be ill. |
| Can’t / Couldn’t | Logical impossibility | That can’t be his car; he doesn’t drive. |
| May / Might / Could | Possibility (50/50 or less) | She might be stuck in traffic. |
⏱️ Deduction about the Past
When our deductions are about events that happened in the past, we add **”have + V3 (past participle)”** to the modal.
- Must have + V3: He must have forgotten about our meeting. (I’m almost sure he forgot.)
- Can’t / Couldn’t have + V3: She can’t have taken my keys; I have them here. (It’s impossible that she took them.)
- May / Might / Could have + V3: They might have arrived earlier than expected. (Maybe they arrived earlier.)
🛠️ How to form them
The structure follows a strict time logic, based on how far away the deduced event is:
| Time | Formula | Example |
|---|---|---|
| Present / State | Modal + Base Form (V1) | He must be tired. |
| Present Continuous | Modal + be + -ing | She might be working. |
| Past (Action) | Modal + have + V3 | He must have left. |
| Past Continuous | Modal + have been + -ing | They might have been sleeping. |
🚫 Common mistakes to avoid
| C1/C2 Mistake ❌ | Correct ✅ |
|---|---|
| He must be gone yesterday. | He must have gone yesterday. (For the past you always need ‘have + V3’!) |
| It can’t be true, he has been dreaming. | It can’t be true; he must have been dreaming. (To explain something that happened before, use ‘must have been’!) |
| She might not have go to the party. | She might not have gone to the party. (After ‘have’ the verb is always the past participle!) |
1. Gap Fill & Translation (C1/C2)
Complete the sentences with the correct modal of deduction (e.g. must have, can’t have, might be).
2. Extra: Sentence Builder 🧩
Tap the words to move them and build perfect deduction sentences!