Precision in Business Communication
Learn to express certainty, probability, and impossibility in the present using the modals must, can't, may, might, and could. Practise applying them in real-world business scenarios to communicate with clarity and confidence.
This mini-course focuses on modal verbs for making logical deductions about the present: must, might, may, could, can't. You will learn how to express what you believe is true, possible, or impossible based on evidence and reasoning.
This course is for intermediate learners who want to express their reasoning and conclusions in English naturally. Whether you are analysing a business situation, interpreting a colleague's behaviour, or drawing conclusions from evidence, deduction modals allow you to communicate your thinking with precision.
Negotiation modals are about politeness and strategy. They control how you say something. For example: "We must finalize the contract before Friday" = expressing a strong obligation or requirement.
Deduction modals are about logic and reasoning. They express what you conclude about a situation. For example: "She must be the manager" = a logical conclusion based on evidence.
The same modal verbs, but a completely different function.
Read these examples. Pay attention to the evidence and how each modal verb expresses a different level of certainty.
a) "She must be the manager. She is giving instructions to everyone."
100% logical certainty: the speaker is sure based on evidence
b) "He can't be serious. That price is ridiculous."
100% logical impossibility: the speaker is sure it is NOT true
c) "They might be stuck in traffic. The meeting started 20 minutes ago."
50% possibility: the speaker is guessing, not sure
d) "She may be working from home today. Her office is empty."
50% possibility: a reasonable guess based on what the speaker observes
e) "He could be at lunch. I saw him leave about an hour ago."
50% possibility: one of several possible explanations
f) "The line must be busy. It keeps going to voicemail."
100% logical certainty: repeated evidence supports this conclusion
g) "They can't be finished already. They only started an hour ago."
100% logical impossibility: the evidence makes this impossible
h) "The CEO might be planning a restructure. There have been a lot of private meetings."
50% possibility: speculation based on indirect evidence
Deduction modals express three levels of certainty about the present:
Think about each question. Then click the answer you think is correct.
Now that you understand the meaning, learn how to build sentences with deduction modals correctly.
The basic pattern for deduction modals in the present:
| Subject | Modal | be | Complement |
|---|---|---|---|
| She | must | be | the manager. (noun) |
| He | can't | be | serious. (adjective) |
| They | might | be | stuck in traffic. (adjective phrase) |
| She | may | be | working from home. (verb-ing) |
| He | could | be | at lunch. (prepositional phrase) |
This is one of the most common mistakes learners make:
| Meaning | Correct | Incorrect |
|---|---|---|
| I am sure it is NOT true | He can't be at work. | He mustn't be at work. |
| Maybe it is not true | She might not be ready. | She can't be ready. (too strong) |
| Modal | Certainty | Example |
|---|---|---|
| must be | 100% certain (positive) | "She must be tired. She worked 12 hours." |
| can't be | 100% certain (negative) | "He can't be 60. He looks so young." |
| may be | ~50% possible (neutral) | "She may be on holiday this week." |
| might be | ~50% possible (slightly less sure) | "He might be looking for a new job." |
| could be | ~50% possible (one of several options) | "It could be a technical problem." |
| might not be | ~50% possibly not | "She might not be aware of the change." |
| may not be | ~50% possibly not | "They may not be ready for the launch." |
How you say a deduction matters as much as the words you choose. Listen to the stress and intonation patterns.
When we are certain (must/can't), the modal and the key word both receive strong stress. The intonation falls.
"She MUST be the MANAGER."
Strong falling intonation on MUST and MANAGER = confidence
"He CAN'T be SERIOUS."
Strong stress on CAN'T and SERIOUS = disbelief
"The line MUST be BUSY."
Falling intonation = the speaker is confident in this conclusion
When we are uncertain (might/may/could), the modal is often unstressed. The intonation can rise slightly, reflecting doubt.
"They might be stuck in TRAFFIC."
"Might" is lighter, stress falls on TRAFFIC. Slight rise at the end = not fully sure.
"She may be working from HOME."
"May" is soft, main stress on HOME. The speaker is guessing.
"He could be at LUNCH."
"Could" is light, stress on LUNCH. This is one possible explanation of many.
"She might not be READY."
"Might not" is gentle. This expresses doubt, not certainty.
Test your understanding with these exercises. Choose the correct modal, fill the gaps, and match situations to deductions.
Read the situation and choose the best modal of deduction.
Complete each sentence with the correct modal: must, can't, might, may, could. Think about the evidence and the level of certainty.
1. "Look at those dark clouds. It be about to rain."
Strong evidence: dark clouds
2. "She has not replied to my email. She be on holiday."
Possible explanation, but not certain
3. "He finished the marathon in under 3 hours. He be very fit."
Strong evidence: finishing a marathon quickly
4. "That restaurant be any good. It is always empty."
Strong evidence against: always empty
5. "Sarah is not at her desk. She be in a meeting."
One possible explanation
6. "He is wearing a very expensive suit. He be quite wealthy."
Reasonable logical conclusion
7. "They be twins. They look completely different."
Strong evidence against: completely different appearance
8. "I heard some noise upstairs. It be the cat."
Possible, but not certain
For each situation, choose the most appropriate deduction.
Look at each scenario. Make at least 2 or 3 deductions about the situation using must, might, may, could, or can't. Then listen to the example answer.
The final challenge: distinguishing deduction from obligation, combining modals with adverbs, and analysing context.
The word "must" has two completely different meanings. Context is the key to understanding which one is used.
| Sentence | Function | How to Tell |
|---|---|---|
| "You must wear a helmet." | Obligation | = It is a rule. You are required to do this. |
| "She must be the manager." | Deduction | = I am almost sure, based on evidence (she is giving instructions). |
| "You must submit the report by Friday." | Obligation | = There is a deadline. It is required. |
| "He must be tired after that flight." | Deduction | = The evidence (long flight) supports this logical conclusion. |
Read each sentence and decide: is "must" used for deduction or obligation?
You can add adverbs to make your deductions more precise:
| Structure | Example | Effect |
|---|---|---|
| must definitely be | "She must definitely be the one in charge." | Strengthens certainty even more |
| could possibly be | "It could possibly be a software bug." | Adds more doubt / tentativeness |
| might well be | "They might well be right about the deadline." | Slightly raises possibility (closer to "probably") |
| could easily be | "This could easily be the best product launch." | Emphasises the reasonableness of this possibility |
Fill in the gaps with the most appropriate modal: must, can't, might, may, could.
A: "James has been in the office since 6 AM."
B: "He be preparing for the quarterly review. It be easy to manage that much data."
A: "Did you notice Lisa has been smiling all day?"
B: "She have received some good news. She be getting the promotion she applied for."
A: "The IT department has cancelled all meetings today."
B: "There be a major system issue. They be dealing with a security breach."
A: "Our competitor just dropped their prices by 40%."
B: "That be sustainable in the long term. They be trying to undercut us before the new product launch."
Now that you have mastered modals of deduction, explore how the same modal verbs work in a completely different context: