Speaking: Grammar in Speaking B2 - Lesson 5: Using Modals for Speculation (must be, might have)

Speaking: Grammar in Speaking B2

Using Modals for Speculation

What you will learn: By the end of this lesson, you will be able to use modals of speculation to express how sure you are about present and past situations.

Speculating about the PRESENT 🤔

Use this structure to make a logical guess about a situation happening now, based on evidence.

~95% Sure (Logical Conclusion)

must be / must + verb

"He's not answering his phone. He must be in a meeting."

~50% Sure (Possibility)

might be / may be / could be

"They might be in the car, or they could be on my desk."

~95% Sure It's Impossible

can't be / can't + verb

"You just had lunch! You can't be hungry again already."

Speculating about the PAST 🔙

Use this structure to make a logical guess about a situation that already happened.

~95% Sure

must have + past participle

"The ground is wet. It must have rained last night."

~50% Sure

might / may / could have + past participle

"He was late for work. He might have gotten stuck in traffic."

~95% Sure It Was Impossible

can't have + past participle

"She got the highest score. She can't have studied very little."

Scenario: The Office Mystery 🕵️

Listen to two colleagues trying to figure out why their manager seems upset. Notice how they use modals to show their level of certainty.

Sophea: "The boss seems really quiet and unhappy today. What's wrong?"

Vannak: "I know. He must be stressed about the upcoming deadline. The project is a little behind schedule." (Present speculation - 95% sure)

Sophea: "That's true. Or he could have received some bad news this morning. He didn't say hello when he came in." (Past speculation - 50% sure)

Vannak: "No, he can't have received bad news. I just saw him smiling. It must be about the project." (Past - 95% impossible; Present - 95% sure)

Grammar Focus ✍️

Common Mistake: `can't` vs. `mustn't`

A very common error is using `mustn't` for negative speculation. We use `mustn't` for strong obligation or prohibition (You mustn't smoke here).

For logical deduction (when you are sure something is impossible), always use can't.

• Incorrect: "That story mustn't be true."
• Correct: "That story can't be true."

Practice Your Skills 🎯

Practice Quiz: How Certain Are You?

1. Your friend didn't come to your party, even though she promised. The next day, you can't reach her. You think, "Something serious __________."

A) might happen
B) must have happened
C) can't have happened

→ Answer: B. You are making a strong logical deduction about a past event based on the evidence.

2. You find a new, expensive-looking pen on the floor of your classroom. It __________ to the teacher, or maybe another student.

A) must belong
B) can't belong
C) could belong

→ Answer: C. You are expressing a possibility, as you are not sure who the owner is.

Key Vocabulary

• Modal of Speculation | កិរិយាស័ព្ទជំនួយសម្រាប់ការសន្និដ្ឋាន
  A modal verb (must, may, might, could, can't) used to make a logical guess.
• Certainty (Noun) | ភាពប្រាកដប្រជា
  The state of being completely sure about something.
• Deduction (Noun) | ការសន្និដ្ឋាន
  A conclusion you reach based on logical reasoning and evidence.
• Punctual (Adjective) | ទៀងពេល
  Doing something or arriving at the correct time; not late.

Your Mission: The Detective Challenge ⭐

Your mission is to practice being a detective and speculating about a situation.

1. Find a simple, unexplained situation. (For example: Your favourite street food vendor isn't in their usual spot today.)
2. Make at least three speculative statements about why, using modals from the lesson to show different levels of certainty.
3. Record yourself for 60 seconds explaining your theories.
   Example: "My usual coffee seller isn't here. She must be sick, because she is always so punctual. Or maybe she could have decided to take a holiday. No, she can't have gone on holiday without telling her regulars. I'm sure she's just sick."