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How did one man write down a language? Must have, might have and can't have for past guesses

This B2 ESL lesson plan teaches must have, might have and can't have through the Cherokee syllabary, which Sequoyah finished by 1821 though he couldn't read English.

Grammar
Modal + have + past participle to guess about the past: must have when you're sure, might, may or could have for maybe, and can't have when you're sure it didn't happen.
Topic
How one man found the syllables of spoken Cherokee, what the sources agree on and what they debate, with words such as syllabary, literate and evidence.
Activities
An explainer, an office argument and a reader's voice memo, self-checking drills, a chat about a fridge note and boxes of guesses.

What's inside

  1. Chapter 1Warm-up: can you write a sound?

    • PictureUnlock
    • Spin the wheel and answerSpin the wheelUnlock
    • Study the words: writing a languageVocabularyTry it
    • Look at the pictures and choose the wordChoose by pictureUnlock

  2. Chapter 2Let's read: talking leaves

    • Look at the picture: a page of talking leavesPictureUnlock
    • Read Leona's explainer on The Why DeskArticleUnlock
    • Read and mark true or falseTrue or falseUnlock
    • Read again and choose the correct answerQuizUnlock
    • Match the paragraphs and the headingsMatchUnlock

  3. Chapter 3Let's listen: books or ears?

    • Listen to Leona and Isaiah in the officeListeningTry it
    • Transcript, for the teacherUnlock
    • Listen and choose the correct answerQuizUnlock
    • Listen to the Reader's Rebuttal: Phil's voice memoListeningUnlock
    • Transcript, for the teacherUnlock
    • Listen and mark true or falseTrue or falseUnlock

  4. Chapter 4Grammar: He must have listened carefully

    • Study the scheme: guesses about the pastGrammar schemeTry it
    • Choose the correct optionChoose the optionTry it
    • Fill in the gaps: use the words in bracketsFill in the gapsUnlock
    • Sort the sentences into the correct columns: how sure is the speaker?Sort into columnsUnlock
    • Choose the correct answer: which sentence fits?QuizUnlock
    • Put the words in the correct orderUnjumbleUnlock

  5. Chapter 5Let's talk: solve it together

    • Choose the right replies: a puzzle on the fridgeChatTry it
    • Open a box and answer: guess what happenedOpen the boxUnlock

  6. Chapter 6Homework

    • Match the words and the meaningsMatchUnlock
    • Unscramble the wordsAnagramUnlock
    • Fill in the gaps with the lesson's wordsFill in the gapsUnlock
    • Find the matching pairs: words and meaningsMemory gameUnlock
    • Choose the correct option: new sentencesChoose the optionUnlock
    • Fill in the gaps: use the words in bracketsFill in the gapsUnlock
    • Choose the correct answer: which deduction fits?QuizUnlock
    • Fill in the table: make a guess from the evidenceFill in the tableUnlock
    • Choose the correct option: ask the guideChoose the optionUnlock
    • Drag the words into the gaps: Isaiah answers PhilDrag and dropUnlock

33 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.

Vocabulary

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

+9 more with pictures and audio in the lessonMore words

  • syllabary
  • literate
  • blacksmith
  • council
  • printing press
  • patience
  • evidence
  • educated guess
  • demonstration

Grammar: past modals of deduction: must have, might have, can't have

Past modals of deduction turn evidence into guesses about the past. Nobody knows exactly how Sequoyah worked out the Cherokee syllables, so the lesson reasons from what is known: He must have listened very carefully. He can't have copied English spelling. Learners pick the modal by how sure they are, then add have and the past participle, which stay the same for every person.

He must have listened. He can't have copied English.

To guess about the past from the evidence, use a modal + have + the past participle. The modal shows how sure you are.

How sure are you? must, might or can't

Must have: you're sure it happened (He must have listened very carefully.). Might, may or could have: maybe it did (He might have seen English books.), and may not have: maybe it didn't. Can't or couldn't have: you're sure it didn't (He can't have copied English spelling.).

How sure are you?

How sure?FormExample
Sure it happenedmust have + past participleHe must have listened very carefully.
Maybe it happenedmight / may / could have + past participleHe might have seen English books.
Maybe it didn't happenmight not / may not have + past participleSome people may not have believed him.
Sure it didn't happencan't / couldn't have + past participleHe can't have copied English spelling.

In the office and in the article

  • He must have listened very carefully to spoken Cherokee.
  • He can't have copied English spelling.
  • He could have borrowed a W and still invented the rest.
  • Both stories might have happened.
  • The first listeners must have been amazed.
  • That must have taken real patience.

Now or in the past?

A guess about now takes the modal and a base form: Isaiah must be tired. A guess about the past adds have + past participle: Isaiah must have been tired last night. In the same way, Harper might know becomes Harper might have known.

A guess about nowA guess about the past
Isaiah must be tired.Isaiah must have been tired last night.
Harper might know the answer.Harper might have known the answer.
That can't be true.That can't have been true.

have + past participle for every person

The form never changes: I must have left, she must have learned, they must have been. It's always have, never has or had, and the participle follows: must have taken, not must have took. No been before a base form: might have listened, not might have been listen.

Every person: the same form

Personmust havemight havecan't have
II must have left my notes at home.I might have seen it before.I can't have lost it.
youYou must have heard the story.You might have read about it.You can't have finished already!
heHe must have listened carefully.He might have seen English books.He can't have copied English spelling.
sheShe must have learned fast.She might have helped him.She can't have known the word.
itIt must have taken years.It might have started as a game.It can't have been easy.
weWe must have missed the bus.We might have met before.We can't have lost the map.
theyThey must have been amazed.They might have doubted him.They can't have read English.

have + the past participle

After the modal, always use have (not has, not had) and the past participle: he must have, they must have; listened, seen, taken, been. Never put been before a base form: He might have listened (not: might have been listen). could have = maybe; couldn't have = sure it didn't happen.

can't have, not mustn't

The opposite of must have is can't have or couldn't have. Mustn't gives a rule, not a guess: You mustn't touch the display. In American English you'll also hear must not have for a strong negative guess: She must not have heard me.

can't have, not mustn't

The opposite of must have is can't have or couldn't have: He never learned English, so he can't have read English books. Mustn't is for rules: You mustn't touch the display. (In American English, you'll also hear must not have for a strong guess: She must not have heard me.)

Say could've, write could have

In fast speech, could have, might have and must have sound like “could of,” “might of” and “must of.” Write have or 've, never of: could've, might've, must've. The common mistakes add must had listened and can't have copy.

Say “could've”, write “could have”

In speech, could have, might have and must have often sound like “could of”, “might of” and “must of”. Write have or 've: could've, might've, must've. Never write “of”.

Common mistakes

  • He must had listened carefully.

    He must have listened carefully.

    always have, not had

  • He can't have copy English spelling.

    He can't have copied English spelling.

    have + past participle

  • He could of borrowed a few shapes.

    He could have borrowed a few shapes.

    write have, not of

  • They might have been listen to him.

    They might have listened to him.

    no been before a base form

More lessons on this grammar: Modal verbs lessons and exercises

Try the past modals of deduction exercises

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

More exercises

What's in the lesson

  • 19 auto-checked exercises
  • 5 games
  • 1 article
  • 1 grammar scheme
  • 1 set of word cards
  • 2 audio clips
  • 2 pictures
  • 2 transcripts

The main objectives of this lesson are to:

  • make a sure guess from the evidence: He found a symbol for every syllable, so he must have listened very carefully.
  • say what maybe happened with might, may or could have: He might have seen a printed Bible. Both stories might have happened.
  • rule something out with can't or couldn't have, not mustn't: He never learned English, so he can't have read English books.
  • use have + past participle for every person: it must have taken, not must had taken, must have took or must of taken
  • solve a puzzle in a chat and guess about the past in class: She can't have reached the top shelf. She must have seen you take them!

Lesson 25 opens Language and communication, unit 7 of English B2.1 · How the World Works. It moves the present guesses of B1.2 lessons 30 and 31 (It must be here, It might be a trick) into the past, alongside lesson 22's should have and could have. Lesson 26 turns to word formation, and lesson 27 adds the continuous and passive forms. The sources can't say exactly how Sequoyah worked, so his story asks for careful guesses.

Students spin a wheel of questions about reading, writing and spelling, then learn twelve words, from syllable and sound out to blacksmith and printing press, with pictures and audio. They read Leona's explainer, which keeps facts apart from guesses, then hear Leona and Isaiah argue over books or ears, and Phil, who is learning the syllabary in Oklahoma, answer back; both are AI-voiced. The grammar chapter has the scheme and five self-checking drills, among them a sort by how sure the speaker is. In the speaking chapter, students solve a puzzle about a note on the fridge in a chat and open boxes of guesses.

All ten homework tasks check themselves: a word match, an anagram, word gaps and a memory game, then forms to choose, gaps from a modal and a verb, a quiz on which deduction fits, a table of guesses from evidence, a museum guide's answers about Sequoyah and Isaiah's reply to Phil with words to drag in.

Grammar:
past modals of deduction · must have · might have · can't have · deductions about the past
Topic:
Sequoyah · the Cherokee syllabary · writing systems · the Cherokee Phoenix · Oklahoma · languages · The Why Desk

Teaching tips

  • Split the board into known and guessed before the explainer. As students read, finished by 1821 goes under known and he might have sounded out words under guessed. Then they name the word that marks each guess.
  • Play the office argument twice: first to decide whose idea wins, Leona's ears or Isaiah's books, then to catch every guess. Students mark each one as sure, maybe or sure it didn't happen.
  • Bring a bag of clues: a bus ticket, a receipt, a shoe with sand in it. Pairs make three guesses about the owner's weekend, one each with must have, might have and can't have.
  • Say the short forms aloud: must've, might've, could've. Then dictate two sentences from the scheme and check that nobody writes could of.

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The whole course: English B2.1 · How the World Works

32 lessons for adults at B2 in American English, each answering one question about how the world works. The team of The Why Desk, a small online magazine in Pittsburgh, takes on one question a week, from the day a computer beat the world chess champion to eight people sealed inside Biosphere 2. Learners tell stories with narrative tenses, speculate about the past and the future, and report what experts claim. The practice exercises check themselves.See the course

  1. Unit 1 AI and the future of work

    narrative tenses, by and until, be bound to and be likely to, the future perfect

    1. Lesson 1Checkmate: the day a computer beat the championNarrative tenses: past simple, past continuous and past perfect
    2. Lesson 2The robot car that crossed the desertTime prepositions: by, until, within, throughout, in time and on time
    3. Lesson 3Can a chatbot fool you?Probability about the future: be bound to, be likely to, the chances are
    4. Lesson 4By 2035, what will AI have designed?The future perfect simple: will have + past participle

  2. Unit 2 Health breakthroughs

    the third conditional, the past perfect and past continuous passive, have something done, the passive with two objects

    1. Lesson 5The moldy melon that changed medicineThe third conditional: if + had done, would have done
    2. Lesson 61.8 million Polio PioneersThe past perfect passive and the past continuous passive
    3. Lesson 7One clinic, many doctorsHave / get something done
    4. Lesson 8A kidney from a twinThe passive with two objects

  3. Unit 3 Moving people

    the past perfect continuous, the passive infinitive and -ing form, it's worth and there's no point, the future in the past

    1. Lesson 9Six years to the golden spikeThe past perfect continuous vs the past perfect simple
    2. Lesson 10Riding a pod with no driverThe passive infinitive and the passive -ing form
    3. Lesson 11The town that painted bike lanes firstIt's worth, there's no point and it's no use + -ing
    4. Lesson 12The highways that were supposed to take 13 yearsThe future in the past

  4. Unit 4 Wildlife comebacks

    reporting verbs with a that clause, with an object and infinitive and with -ing, verbs of perception

    1. Lesson 13Did wolves really change Yellowstone's rivers?Reporting verbs + that clause
    2. Lesson 14Bringing a parrot back from the edgeReporting verbs + object + (not) to + base form
    3. Lesson 15The beavers that came by parachuteReporting verbs + -ing and verb + preposition + -ing
    4. Lesson 16Fifteen bison take the trainVerbs of perception + object + base form or -ing

  5. Unit 5 Pop culture goes global

    comment adverbs, wish and if only for the present and the past, have someone do and get someone to do

    1. Lesson 17The party that started hip hopComment adverbs: apparently, supposedly, undoubtedly
    2. Lesson 18Slide to the left!Wish and if only for wishes about now
    3. Lesson 19If only they'd kept SupermanWish and if only + past perfect for regrets
    4. Lesson 20The hit factory on West Grand BoulevardCausative have and get: have someone do, get someone to do

  6. Unit 6 Money and smart choices

    -ever words and no matter, should have and could have, prepositions for numbers and change, it's time and would rather

    1. Lesson 21The bank that never closed-ever words and no matter
    2. Lesson 22One marshmallow now or two later?Should have, shouldn't have and could have
    3. Lesson 23Benjamin Franklin's 200-year giftPrepositions for numbers and change
    4. Lesson 24Why buy a drill you'll use once?It's (high) time and would rather + past simple

  7. Unit 7 Language and communication

    must have, might have and can't have, verb prefixes and suffixes, past modals in continuous and passive forms, agreement with quantities

    1. Lesson 25 · you're hereHow did one man write down a language?Past modals of deduction: must have, might have, can't have
    2. Lesson 26Why do Americans write “color”?Verb prefixes and suffixes: misspell, rewrite, simplify, shorten
    3. Lesson 27The joke that needed a smileyPast modals in continuous and passive forms
    4. Lesson 28Can preschoolers save a language?Subject-verb agreement with quantities and collective nouns

  8. Unit 8 Exploring the extremes

    dimension nouns, the future continuous and future perfect continuous, compound adjectives, only, even and just

    1. Lesson 29A walk on the ocean floorDimension nouns and phrases: depth, width, height
    2. Lesson 30Six months of night at the South PoleThe future continuous and the future perfect continuous
    3. Lesson 31Flying on pedal powerCompound adjectives with numbers and participles
    4. Lesson 32Two years under glassFocus adverbs: only, even, just and at all

Questions about this lesson

What does “must have” mean?
Must have + past participle shows that you're almost sure something happened, because the evidence points to it: He found a symbol for every syllable, so he must have listened very carefully. You didn't see it happen; you worked it out. The B2 lesson How did one man write down a language? on edio.ai teaches it with Sequoyah, whose exact method nobody knows.
How do you form past modals of deduction?
Use a modal, then have, then the past participle: must have listened, might have seen, can't have copied. The form is the same for every person: I, she and they must have been. The modal shows how sure you are: must for sure, might, may or could for maybe, can't or couldn't for sure it didn't happen. The scheme in How did one man write down a language? on edio.ai sets the four levels in one table.
What's the difference between “must have” and “might have”?
It's how sure you are. Must have is a strong conclusion from clear evidence: It took about twelve years, so it must have taken real patience. Might have is one possibility among others: He might have seen a printed Bible. In How did one man write down a language? on edio.ai, students sort sentences into three columns: sure it happened, maybe it happened and sure it didn't.
What's the difference between “must have” and “should have”?
Must have guesses what happened: She must have left early. Should have says what would have been right but didn't happen, often as a regret: I should have left early. One is a deduction, the other a judgment. On edio.ai, should have comes first, in B2.1 lesson 22, and How did one man write down a language?, lesson 25, adds the guesses.
Is it “mustn't have” or “can't have”?
For a past thing you're sure didn't happen, use can't have or couldn't have: He never learned English, so he can't have read English books. Mustn't is for rules, as in You mustn't touch the display. Americans also say must not have for a strong negative guess (She must not have heard me), so How did one man write down a language? on edio.ai never marks it wrong, but it drills can't have.
Who was Sequoyah?
Sequoyah was a Cherokee man who gave Cherokee its own writing. He spoke only Cherokee and never learned to read or write English; he worked as a hunter, fur trader, blacksmith and silversmith. Around 1809 he began a writing system, and by 1821 it was finished. Within a few years, thousands of Cherokee people could read and write it. Leona's explainer in How did one man write down a language? on edio.ai tells the story.
What is the Cherokee syllabary?
It's a writing system with one symbol for each syllable, such as la or a, not an alphabet. There are about 85 symbols. Some look like Latin letters but stand for other sounds: Ꮃ looks like a W but says la. The Cherokee Phoenix newspaper used it from 1828, and today it's on phones and street signs, as How did one man write down a language? on edio.ai shows.
How do I teach past modals of deduction to B2 students?
Start from a real puzzle with missing evidence, so the guesses matter, and let students sort statements into known and guessed. Then build the scale: sure it happened, maybe, sure it didn't. How did one man write down a language? on edio.ai moves from Leona's explainer, which marks its guesses, to the office argument, the scheme, a sort by certainty and a word-order drill.
What's a good game for practicing must have and might have?
Try a detective round: show a scene with clues, such as a messy kitchen or a wet umbrella by the door, and teams score a point for each correct guess: Someone must have cooked. It can't have been sunny. One of the boxes in How did one man write down a language? on edio.ai asks for three guesses about the classroom this morning, with must have, might have and can't have.
What's good homework for past modals of deduction?
Good homework pairs each guess with its evidence: There's sand in Harper's shoes leads to She must have walked on the riverbank. Add form choices and a quiz on how sure the speaker is. All ten homework tasks in How did one man write down a language? on edio.ai check themselves, ending with a museum guide's answers about Sequoyah and Isaiah's reply to a reader.
How do you practice past modals of deduction one-to-one?
Swap small mysteries: the teacher gives a clue, such as a full mug of cold coffee, and the student explains it with must have, might have or can't have, then sets a clue for the teacher. The chat in How did one man write down a language? on edio.ai works without a partner: Chad's six-year-old sister has left a note in symbols, and the student works out what it meant.
Are there interactive exercises for past modals of deduction?
Yes. With no account, this page plays three parts of How did one man write down a language?, a B2 lesson on edio.ai: the office argument about how Sequoyah did it; a drill of eight sentences where students choose the form; and the chat about a note on the fridge. Everything else needs an account.
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