When you guess what's probably true
You're watching a film. You see this scene: A woman rushes into a coffee shop, soaking wet, checking her watch every two seconds. The man already there looks confused.
Without overthinking — what would you say about this moment? What do you think is probably true?
There's no "correct" answer here. You're making educated guesses with the information you have. We all do this constantly in real life — so let's name it and own it.
Every day you make educated guesses: "He must be angry" (based on his tone). "She can't be serious" (based on what you know about her). "It might rain" (based on the sky). This is called logical deduction — and in English, we have specific modal verbs that signal HOW SURE we are.
Without them, you say: "I think he is angry." With them: "He must be angry" — and native speakers hear that you've thought about the evidence.
These verbs help you make logical guesses about what's happening right now.
Watch how certainty changes with different modals:
MUST / CAN'T — This is the only logical conclusion
COULD / MAY — This is possible given the facts
MIGHT — This is one possibility among others
| Modal | Meaning | Example |
|---|---|---|
| must | Logical deduction: This is almost certainly true Based on facts, there's only one answer |
"She hasn't answered in 3 days. She must be very busy." |
| can't | Logical deduction: This is almost certainly FALSE The facts make it impossible |
"He finished a 5-hour exam in 20 minutes. He can't have understood it." |
| could | Logical deduction: This is POSSIBLE It fits the facts, but so do other possibilities |
"They're not answering. They could be in a meeting, or they could be sleeping." |
| may | Logical deduction: This is POSSIBLE More formal than "could" — same meaning, more cautious tone |
"It may rain tomorrow, but the forecast is uncertain." |
| might | Logical deduction: This is POSSIBLE but LESS LIKELY One possibility, but other things are more probable |
"I might get the promotion, but I don't expect it." |
Situation: It's 8 pm. Sarah's phone goes to voicemail. She hasn't been online for 6 hours.
She must be sleeping — 8pm + no online = sleep is the logical conclusion
She could be at the gym — possible, fits the facts, but not the only answer
She might be on vacation — possible, but less likely given the time and context
I'm going to model HOW to think about deduction. Then we'll do one together.
Scenario: A friend emails: "I won't be at tomorrow's meeting. Something unexpected came up. I'll explain later."
What do I know?
What can I deduce?
I use the facts to narrow down what's probably true, then pick the right modal to show how confident I am.
Scenario: You're in a café. A woman is sitting alone at a table for two. She keeps checking her phone. Her coffee is getting cold. She looks frustrated.
Don't worry about being perfect. I want to hear YOUR thinking. How are you using the facts to make a guess?
Three scenarios. Pick one, two, or all three. For each situation, make THREE deductions using must, can't, could, may, or might.
The situation:
A teenager has been in their bedroom for 6 hours. Their gaming headset is on. Parents haven't heard them come out. Dinner was ready an hour ago and nobody has eaten it.
The situation:
Your colleague is usually chatty at work. Today they're very quiet. They've made three mistakes in emails. They keep looking out the window. They turned down lunch with everyone.
The situation:
Your friend texts at 3 am: "Can't sleep. Mind's racing." They have a job interview tomorrow. They haven't slept properly in weeks.
Remember: Use facts. Don't just guess. Say "MUST" when there's only one logical answer. Say "COULD" when other things are possible too. Say "MIGHT" when it's less likely but still possible.
The same logic applies to the past — but the structure changes. You use modal + have + past participle.
Compare present and past:
Now
He must be angry
modal + base verb
Before
He must have been angry
modal + have + past participle
The logic is identical. You're still using facts to make an educated guess. The only difference is WHEN — now (present) or before (past).
| Modal | Present vs Past | Example |
|---|---|---|
| must have | He must be late → He must have been late | "She didn't call. She must have forgotten my number." |
| can't have | It can't be true → It can't have been true | "He said he was at home. But his car was gone. He can't have been there." |
| could have | She could be there → She could have been there | "I didn't see him. But he could have arrived late." |
| may have | It may be true → It may have been true | "Nobody knows why she left. She may have had a family emergency." |
| might have | He might come → He might have come | "He didn't show up. He might have gotten sick." |
Situation: Your friend was supposed to meet you at 6 pm. They never showed up. They didn't text. Two hours later, they texted: "I'm so sorry. Bad day."
must have
"They must have forgotten" — they didn't text, so they probably just forgot the time.
can't have
"They can't have ignored the message" — they said they had a bad day, so they weren't choosing to avoid me.
could have
"They could have been in an accident" — possible, but their "bad day" message suggests something else.
might have
"They might have had a family emergency" — possible, but they would probably have mentioned it.
Here's a longer scenario. You'll make deductions about BOTH what's happening now and what happened before.
You bump into an old friend. They look exhausted. They're wearing work clothes at 9 pm on a Saturday. They say: "It's been a crazy week. I don't even remember the last time I had a day off." When you ask what's wrong, they become vague: "Just... a lot happening. I don't want to talk about it right now."
Without scrolling back, answer these from memory.
What's the difference between "She must be there" and "She could be there"? When would you use each one?
Must: Only one logical conclusion from the facts
Could: One possibility among several — the facts fit it, but other things are possible too
How do you structure a past deduction? Give an example with "must have."
Structure: modal + have + past participle
Example: "He must have left early" or "They must have forgotten"
Rank these by certainty (most sure to least sure): might, must, could, can't
Most to least certain: must, can't, could, might
(Must/can't show certainty. Could shows possibility. Might shows lowest certainty.)
You see your friend wearing a heavy coat in summer. They look cold. Is this more "must be" or "might be"? Why?
Could be either:
"They must be cold" if you're certain from the evidence (they're shivering, wrapped up tight)
"They might be cold" if there could be other reasons (it's actually cool, they just like coats, etc.)
In the next lesson, we'll deepen this with: