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Working Across Cultures: must have and can't have for clearing up misunderstandings

This B2 Business English lesson plan on cross-cultural communication teaches must have and can't have for working out what a partner meant.

Grammar
Deduction now (She must be new.) and in the past (They must have thought there was no hurry.), from must to can't, and the two meanings of must.
Topic
Direct and indirect communication between partner companies, from a polite if possible to a two-line email, with idioms like read between the lines and beat around the bush.
Activities
An article on communication styles, a call clearing up two mix-ups, self-checking drills, a chat and a wheel of clues, then an email and a recorded story.

What's inside

  1. Chapter 1Warm-up: What Did They Mean?

    • PictureUnlock
    • Open a box and discussOpen the boxUnlock
    • Study the vocabulary: clear communicationVocabularyTry it
    • Match the phrases to the situationsMatchUnlock

  2. Chapter 2Reading: Small Words, Big Misunderstandings

    • Read the article: Direct or indirect? Small words, big misunderstandingsArticleUnlock
    • True or false? Check the articleTrue or falseUnlock
    • Choose the correct answer: the articleQuizUnlock

  3. Chapter 3Listening: Two Small Mysteries

    • Listen to Priya and Daniel's callListeningTry it
    • Transcript, for the teacherUnlock
    • Choose the correct answer: two small mysteriesQuizUnlock

  4. Chapter 4Grammar: They Must Have Thought…

    • Study the scheme: modals of deductionGrammar schemeTry it
    • Choose the correct option: how sure are you now?Choose the optionUnlock
    • Choose the correct option: what must have happened?Choose the optionUnlock
    • Fill in the gaps: modal + have + past participleFill in the gapsTry it
    • Fill in the table: say it with a modal verbFill in the tableUnlock
    • Choose the correct answer: sure, possible or necessary?QuizUnlock

  5. Chapter 5Speaking: Read the Clues

    • Choose the best replyChatTry it
    • Spin the wheel and discussSpin the wheelUnlock

  6. Chapter 6Homework: Clear the Air

    • Choose the correct option: deductions at workChoose the optionUnlock
    • Find the matching pairs: phrases and meaningsMemory gameUnlock
    • Write an email that clears up a misunderstandingWriting, checked by the teacherUnlock
    • Record a story about a misunderstandingSpeaking, checked by the teacherUnlock

22 exercises in 6 chapters. Start a 7-day free trial to open all of them, copy any part into your own lessons, and teach the lesson live.

Communication idioms

10 words and phrases from the lesson, each with a picture and audio in edio.

+7 more with pictures and audio in the lessonMore words

  • read too much into something
  • spell it out
  • beat around the bush
  • a firm deadline
  • clear the air
  • give someone the benefit of the doubt
  • be on the same page

Grammar: modals of deduction, present and past

When a partner's message seems odd, deduction is a fairer first step than blame. With modal verbs, learners say how sure they are, from must to can't, about what is true now and what happened before, and build each guess on evidence: a late report, a two-line email, a train announcement on a call.

Modals of deduction: present and past

How to say how sure you are about what is true now or what happened before

Now: must, might or can't + base form

For the present, the modal takes the base form: You must know him well (sure), He might be in a meeting (perhaps), That long email can't be from Daniel (sure it isn't). For an action happening now, add be + -ing: He must be traveling.

How sure?UseExample
I'm sure it's true.must + base formYou've worked with Daniel for a year. You must know him well.
Perhaps it's true.might / may / could + base formHe isn't answering. He might be in a meeting.
Perhaps it isn't true.might not / may not + base formIt's only eight. He may not be at his desk yet.
I'm sure it isn't true.can't + base formThat long email can't be from Daniel. He never writes more than five lines.
I'm almost sure it isn't true.must not + base form (common in American English)His light is off. He must not be at his desk.
It's happening now.must / might / can't + be + -ingI can hear a train. He must be traveling.

Before now: modal + have + past participle

For the past, add have and the past participle: They must have thought it was optional. The invoice might have gone to the wrong person. He can't have been angry. An action in progress takes have been + -ing: They must have been expecting it earlier.

How sure?UseExample
I'm sure it happened.must have + past participleThe report came a week late. They must have thought it was optional.
Perhaps it happened.might / may / could have + past participleThe invoice might have gone to the wrong person.
Perhaps it didn't happen.might not / may not have + past participleHe may not have seen my email yet.
I'm sure it didn't happen.can't have / couldn't have + past participleHe can't have been angry. He ended with "Best wishes".
I'm almost sure it didn't happen.must not have + past participle (American English)He must not have seen my email.
It was in progress.must / might / can't have been + -ingThey must have been expecting it earlier.

Must: I'm sure, or it's a rule?

You must be tired after the flight is a deduction; Visitors must sign in at reception is a rule. For deduction, the opposite is can't, or in American English must not (He must not be at his desk); for a rule, must not means it isn't allowed.

must = I'm sure (deduction)

  • You must be tired after the flight.
  • They must have misread my email.
  • The opposite is can't (or, in American English, must not): That can't be right.

must = it's necessary (obligation)

  • Visitors must sign in at reception.
  • Invoices must show the order number.
  • Must not can also mean it's not allowed: You must not share your password.

Could, might or may for one situation

For one specific case, use could, might or may: The invoice could be in your spam folder. Can is for what's possible in general (Short emails can sound rude), and can have isn't used for a past possibility. In deduction, could have means perhaps, not criticism.

Can or could?

For one specific situation, use could, might or may: The invoice could be in your spam folder. Can is for what is possible in general: Short emails can sound rude. In the past, use could have, might have or may have for a possibility, not can have: It could have gone to spam.

Could have: possible, not criticism

You know could have for criticism: You could have told me! Here it means perhaps: The email could have gone to the wrong person. The situation tells you which meaning it is.

Check the form, then the evidence

Three form errors are common: must had, may have went and must to be. Then check the meaning: two possible answers mean you aren't sure, so use might, not must; and if nobody told her, She can't have known.

Typical mistakes: forms

  • They must had forgotten.

    They must have forgotten.

    Modal + have, never had.

  • She may have went home.

    She may have gone home.

    Have + the past participle: gone, not went.

  • He must to be busy.

    He must be busy.

    No to after must, might, may, could or can't.

  • They must have expecting it.

    They must have been expecting it.

    An action in progress: have been + -ing.

Typical mistakes: meaning

  • He must be in a meeting, or perhaps he's at lunch.

    He might be in a meeting, or perhaps he's at lunch.

    Two possible answers mean you aren't sure: might, may or could, not must.

  • The email can have gone to spam.

    The email could have gone to spam.

    A past possibility: could, might or may have.

  • That can be Daniel on the phone.

    That could be Daniel on the phone.

    One specific situation: could, might or may.

  • She must have known. Nobody told her.

    She can't have known. Nobody told her.

    Check the evidence: nobody told her, so you're sure she didn't know.

More lessons on this grammar: Modal verbs lessons and exercises

Try the must have and can't have exercises

Try them yourself: these are the same exercises your students do in edio.

More exercises

What's in the lesson

  • 11 auto-checked exercises
  • 3 games
  • 2 teacher-checked tasks
  • 1 article
  • 1 grammar scheme
  • 1 set of word cards
  • 1 audio clip
  • 1 picture
  • 1 transcript

The main objectives of this lesson are to:

  • say how sure you are about the past: They must have thought it was optional. It might have sounded optional. She can't have known.
  • make deductions about now, including actions in progress: She must be new. He must be traveling. That can't be right.
  • tell must for deduction from must for a rule, and use could, not can, for one possibility: The invoice could be in your spam folder.
  • write an email that clears up a misunderstanding without blaming anyone, and suggest one simple rule for the future

Lesson 18 sits second in Looking back and ahead, the last unit of Business English B2 · A Year at Wrenfield, set at a fictional Portland coffee roaster that reviews its year and works with partners abroad. Its modals come from lesson 15, where must stated a rule, and lesson 16's should have and could have; here they say how sure the speaker is. Lesson 19 turns to the causative. Between partners, a guess like They must have read it as optional keeps a small misunderstanding from turning into a complaint.

Open boxes ask how learners soften requests and read short emails; ten word cards with pictures and audio, from read between the lines to be on the same page, are then matched to situations. An article compares direct and indirect styles and offers five habits that help. In the AI-voiced call, a finance director and a distributor from Germany solve two small mysteries: a report that came a week late after a polite if possible, and a two-line email that worried a new assistant.

Five self-checking exercises follow the scheme, among them a table that turns I'm sure and perhaps into modals. In the chat, students help a colleague work out a hotel partner's puzzling message, and a wheel deals out clues to explain, opinions and a role-play. Homework drills deductions at work and adds a memory game, both self-checking; an email that clears up a misunderstanding and a recorded story about one go to the teacher.

Grammar:
modals of deduction · must have done · can't have done · might have done
Topic:
working across cultures · communication styles · misunderstandings at work

Teaching tips

  • Ask what if possible means before the reading: a real deadline or a nice extra? Mixed answers in the room show the very problem the article describes.
  • Pause the call after each mystery and let learners deduce before the speakers do (They must have…, She can't have…), then play on and compare.
  • Keep styles about people and companies, not countries: as the article does, ask where styles differ between departments or colleagues, so the talk doesn't harden into stereotypes.
  • Bring a real short email, names removed, to an in-company group or a one-to-one client: they guess how it might have come across, then rewrite it to spell out what the writer needs.

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The whole course: Business English B2 · A Year at Wrenfield

20 lessons at B2 in American English that follow a year at Wrenfield Coffee Roasters in Portland, Oregon, as founder Claire Morgan and her team win a Dutch hotel contract. Learners network, write emails, run meetings, negotiate, handle complaints and present figures, with one grammar point per lesson.See the course

  1. Unit 1 First contacts

    networking, a company story, a business lunch and emails: present tenses, the present perfect, question tags, indirect questions

    1. Lesson 1Making ContactsPresent simple and present continuous at work
    2. Lesson 2Our Story: From Cart to RoasteryPresent perfect and past simple for company history
    3. Lesson 3The Business LunchQuestion tags and short answers
    4. Lesson 4Emails That Get AnswersIndirect questions and polite requests

  2. Unit 2 Meetings and figures

    scheduling, sales figures, running a meeting and negotiating: future forms, trends, gerunds and infinitives, conditionals

    1. Lesson 5Setting Up MeetingsFuture forms for meetings and schedules
    2. Lesson 6The Monthly FiguresDescribing trends
    3. Lesson 7Running a MeetingGerunds and infinitives in meetings
    4. Lesson 8Negotiating a DealFirst and second conditionals in a negotiation

  3. Unit 3 Problems and growth

    a complaint, a late shipment, a launch and hiring: the present perfect continuous, the passive, comparatives, relative clauses

    1. Lesson 9Handling a ComplaintPresent perfect simple vs continuous
    2. Lesson 10The Late ShipmentThe passive in all tenses
    3. Lesson 11Launching a ProductComparatives and superlatives with modifiers
    4. Lesson 12Hiring the Right PersonDefining and non-defining relative clauses

  4. Unit 4 Reports, prices and feedback

    reporting back, explaining prices, expenses and feedback: reported speech, linking words, modals of obligation, past modals

    1. Lesson 13Reporting BackSay vs tell in reported speech
    2. Lesson 14Explaining PricesLinking words of contrast, cause and result
    3. Lesson 15Travel and Expenses: Can I Claim That?Modals of obligation, prohibition and permission
    4. Lesson 16Giving FeedbackShould have, could have and didn't need to

  5. Unit 5 Looking back and ahead

    what went wrong, other cultures, an agency and next year: the third and mixed conditionals, past deduction, the causative, the future perfect

    1. Lesson 17What Went WrongThird and mixed conditionals
    2. Lesson 18 · you're hereWorking Across CulturesModals of deduction, present and past
    3. Lesson 19Working with an AgencyCausative have and get
    4. Lesson 20The Road AheadFuture continuous and future perfect

Questions about this lesson

How can you avoid misunderstandings in cross-cultural communication?
To avoid cross-cultural misunderstandings, say exactly what you need, and check before you react. If a date is a firm deadline, write We need it by Friday at noon, and keep if possible for things that really are optional. Don't read too much into a short reply; it usually means the writer is busy. Agree early with a new partner how you'll show urgency, and clear up any mix-up on a short call.
What's the difference between "must have done" and "might have done"?
Must have done means you're sure it happened; might have done means perhaps. The report came a week late. They must have thought it was optional. But: I'm not sure why the courier was late. He might have gotten stuck in traffic. For the opposite of must have, use can't have: He can't have been angry. The B2 lesson Working Across Cultures on edio.ai sets these out by how sure the speaker is.
What are the two meanings of "must"?
Must can mean I'm sure it's true, or it's necessary. You must be tired after the flight is a deduction; Visitors must sign in at reception is a rule, and the situation tells them apart. Only the deduction has a past with must have (They must have misread my email); for a past obligation, use had to. A quiz in Working Across Cultures, a B2 lesson on edio.ai, asks which meaning each sentence has.
Is it "can have" or "could have" for a past possibility?
Use could have, might have or may have, not can have: The email could have gone to spam. The present follows a similar rule: could for one specific situation (That could be Daniel on the phone), can for what's possible in general (Short emails can sound rude). Only the negative works with can: He can't have seen it means you're sure he didn't.
What does "beat around the bush" mean?
To beat around the bush is to avoid saying what you really mean, talking around the point instead. Sam talked for ten minutes before finally saying that the campaign was over budget. It's the American form; British English often says beat about the bush. Direct people may feel that indirect colleagues beat around the bush, when they're only trying to be polite. The fix is to spell it out.
What does "read between the lines" mean?
To read between the lines is to find a meaning that a message doesn't state. A client who calls a proposal an interesting idea may not really like it, and a careful reader picks that up. Indirect writers often expect it; direct readers may not, and take if possible as optional. When it matters, ask: Just to be sure, is Friday a firm deadline? It's the first of ten word cards in Working Across Cultures on edio.ai.
What's the difference between direct and indirect communication?
Direct communication says exactly what it means; indirect communication softens it. Please send the figures by Friday is direct; Could we possibly have the figures by Friday? is indirect and expects the reader to read between the lines. Neither style is better, and neither belongs to a country: companies, departments and even two people in one office can differ. Trouble starts when we judge others' words by our own rules.
How do cultural differences in business show up in emails?
Mostly in how directly people ask, say no and show urgency. A polite if possible can read as optional to a direct reader, so a report arrives a week late; a two-line email with no greeting can seem angry to an indirect reader when the writer is just busy. Give people the benefit of the doubt, and agree with a new partner how you'll mark something as urgent.
What does "give someone the benefit of the doubt" mean?
To give someone the benefit of the doubt is to believe they meant well, even without proof. When a short reply seems rude, assume the writer is busy, not annoyed: The reply was short, but let's give him the benefit of the doubt. He must be busy this week. Together with asking before you react, it keeps partners on the same page after a message that could be read two ways.
How do I teach cross-cultural communication in a business English class?
Work from small, real misunderstandings, not national stereotypes: a polite request read as optional, a short email read as angry. Learners say what each side must have thought, rewrite the message in the other style and agree on a rule, such as a clear date means a deadline. In Working Across Cultures on edio.ai, a call between two partners solves two such mysteries and ends with two rules.
What's good homework for practicing deductions about the past?
A useful task is an email that clears up a misunderstanding without blame: You must have thought the deadline was flexible. My email can't have been clear enough. Ask for at least three modals of deduction and one rule for the future. The B2 lesson Working Across Cultures on edio.ai sets this very email, plus a recorded story about a misunderstanding, for the teacher to review; a drill and a memory game check themselves.
Are there interactive exercises for deductions about the past?
Yes: gap-fills that build modal + have + past participle check every form as it's typed. Three parts of Working Across Cultures, a B2 Business English lesson on edio.ai, play on this page without an account: a call that solves two workplace mysteries, a gap-fill from must have thought to couldn't have read, and a chat working out what a hotel partner's message means. The other exercises are locked.
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