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It must be here somewhere! Must and can't for sure guesses about now

This B1 ESL lesson plan teaches modals of deduction, must be and can't be for sure guesses about now, with geocaching, the GPS treasure hunt.

Grammar
Must + base form when clues make you sure (It must be under the bench.), can't when you're sure it isn't true, must be + -ing for now, and mustn't kept for rules.
Topic
Geocaching, from the first cache hidden in Oregon in 2000 to millions of caches today, with words such as coordinates, hollow and trinket.
Activities
Episode notes to read, a hunt in a park and a listener's challenge to hear, self-checking drills, a chat that follows clues and open boxes.

What's inside

  1. Chapter 1Warm-up: where did I put it?

    • PictureUnlock
    • Spin the wheel and answerSpin the wheelUnlock
    • Study the words: the treasure huntVocabularyTry it
    • Look at the pictures and chooseChoose by pictureUnlock

  2. Chapter 2Let's read: a bucket in the woods

    • Look at the picture: a bucket in the woodsPictureUnlock
    • Read the episode notesArticleUnlock
    • Read and mark true or falseTrue or falseUnlock
    • Read again and choose the correct answerQuizUnlock

  3. Chapter 3Let's listen: the hunt in the park

    • Listen to Jade and DariusListeningTry it
    • Transcript, for the teacherUnlock
    • Listen and choose the correct answerQuizUnlock
    • Listen to the Listener's Take: Nelson's messageListeningUnlock
    • Transcript, for the teacherUnlock
    • Listen and mark true or falseTrue or falseUnlock

  4. Chapter 4Grammar: It must be here, it can't be there

    • Study the scheme: must and can't for guessesGrammar schemeTry it
    • Choose the correct optionChoose the optionUnlock
    • Fill in the gaps: must or can't + the base formFill in the gapsTry it
    • Fill in the gaps: must be or can't be + -ingFill in the gapsUnlock
    • Fill in the table: must or can'tFill in the tableUnlock
    • Choose the correct answerQuizUnlock

  5. Chapter 5Let's talk: follow the clues

    • Choose the right replies: follow the cluesChatTry it
    • Open a box and answerOpen 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
    • Sort the words into the correct columnsSort into columnsUnlock
    • Choose the correct option: new sentencesChoose the optionUnlock
    • Fill in the gaps: say it with must or can'tFill in the gapsUnlock
    • Put the words in the correct orderUnjumbleUnlock
    • Choose the correct answer: the best guessQuizUnlock
    • Choose the correct option: a cache page and its logsChoose the optionUnlock
    • Drag the words into the gaps: the hosts' answer to NelsonDrag and dropUnlock

32 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

  • coordinates
  • hint
  • hollow
  • moss
  • pond
  • bush
  • compass
  • trinket
  • plaque

Grammar: must and can't for deduction

Must and can't are for guesses about now when the clues make you almost sure: It must be under the bench. It can't be in the pond. On a geocache hunt, students back up every guess with a clue, add be + -ing for what is happening now, and keep mustn't for rules.

It must be here! It can't be there!

Use must and can't for guesses about now, when clues make you almost sure. must = I'm sure it's true. can't = I'm sure it isn't true.

Sure it's true, sure it isn't

Must + base form means you're sure it's true: It must be under the bench. Can't (or couldn't) means you're sure it isn't: It can't be in the pond. For an action happening now, add be + -ing: They must be looking for it.

How sure?FormExample
I'm sure it's true.must + base formThe arrow points at the bench. It must be under it.
I'm sure it isn't true.can't (or couldn't) + base formThe cache stays dry. It can't be in the pond.
I'm sure it's happening now.must be + -ingThose kids have a phone out. They must be looking for it too.
I'm sure it isn't happening now.can't be + -ingFootnote is meowing. She can't be sleeping.

The same form for every person

Must and can't never change, and the verb after them is the base form: He must know, not must knows; It must be, not must to be or must is. No to and no -s after either modal: You can't be serious!

The same form for every person

Personmustcan'tmust be + -ing
II must be lost.I can't be wrong!I must be dreaming!
youYou must know this park.You can't be serious!You must be joking!
heHe must be hungry.He can't be tired.He must be recording.
sheShe must live near here.She can't be at home.She must be sleeping.
itIt must be under the bench.It can't be in the pond.It must be raining.
weWe must be close.We can't be far.We must be walking the wrong way.
theyThey must love puzzles.They can't be lost.They must be looking for it.

must and can't + the base form

After must and can't, use the base form, with no to and no -s: It must be (not: must to be, must is). It can't be (not: can't to be). He must know (not: must knows). For something happening now, use must be + -ing: They must be looking (not: must looking).

A rule or a guess?

From A2, must and mustn't give rules: You mustn't take the cache home. In a guess, must stays, but the sure “no” guess is can't, not mustn't. And can without not is for things that are sometimes possible: Caches can be tiny.

A rule or a guess?

Rules (from A2): must / mustn't

  • You must sign the logbook.
  • You mustn't put food in a cache.
  • You mustn't take the cache home.

Sure guesses (new): must / can't

  • It must be under the bench.
  • It can't be in the pond.
  • They must be looking for it.

can't, must not or mustn't?

can't = I'm sure it isn't true: It can't be in the pond. must not (two words) is a “no” guess too, a little less sure: Nobody signs the log. People must not know this place. The short form mustn't is for rules: You mustn't take it home. can without not is for things that are sometimes possible (Caches can be tiny), not for one guess now: It must be in the log.

In the park and in the story

Each example pairs a clue with a guess: Nelson's cache is a nano, so it must be really tiny. Darius ate a sandwich ten minutes ago. He can't be hungry again! The clue comes first, then the guess.

  • Somewhere near you, there must be a geocache.
  • The cache page says it stays dry, so it can't be in the pond.
  • Those two kids must be looking for it too!
  • The first bucket can't be at the spot today: a mower damaged it.
  • Nelson's cache is a nano, so it must be really tiny.
  • Darius ate a sandwich ten minutes ago. He can't be hungry again!

Common mistakes

  • The cache stays dry, so it mustn't be in the pond.

    The cache stays dry, so it can't be in the pond.

    a sure “no” guess: can't (the short form mustn't is for rules)

  • It must to be under the bench.

    It must be under the bench.

    no to after must

  • It must is in the log.

    It must be in the log.

    must + base form

  • Someone must looking for it.

    Someone must be looking for it.

    happening now: must be + -ing

More lessons on this grammar: Modal verbs lessons and exercises

Try the 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
  • 4 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 sure guesses with must + base form: The arrow points at the bench. It must be under it. You must know this park.
  • say what can't be true: The cache page says it stays dry, so it can't be in the pond.
  • guess what is happening now with must be + -ing: Those two kids must be looking for it too!
  • tell a guess from a rule: It must be under the bench is a guess, and You mustn't take the cache home is a rule

Lesson 30 is the second lesson of Adventure and challenge, unit 8 of English B1.2 · Changemakers. It builds on A2.2 lesson 22, where must and mustn't gave rules, and on the present continuous behind must be looking. Lesson 31 adds might, may and could for guesses that are less sure. A treasure hunt, where each clue narrows down the hiding place, runs on sure guesses.

Students spin a wheel of questions about treasure hunts, lost keys and mysteries, then learn twelve words, from stash and swap to plaque, with pictures and audio. They read the episode notes on the first geocache, hidden in Oregon in 2000, then hear Jade and Darius hunt for a cache in a Kansas City park and a challenge from Nelson, a listener in Oregon, both AI-voiced. The grammar chapter has the scheme and five self-checking drills, among them a table that turns each clue into two guesses. In the speaking chapter, students follow Estelle's clues in a chat, then open boxes of guessing prompts.

All ten homework tasks check themselves: a word match, an anagram, a word gap-fill and a column sort, then a choice of forms, sentences to rewrite with must or can't, word order, a best-guess quiz, a cache page with its logs and the hosts' answer to Nelson with words to drag.

Grammar:
modals of deduction · must for deduction · can't for deduction · must be + -ing
Topic:
geocaching · GPS · Oregon · treasure hunts · the outdoors · Kansas City · Stories That Travel

Teaching tips

  • Hide something in the classroom before the lesson, then give clues one at a time. Students guess aloud after each one: It can't be in the desk. It must be near the window.
  • Before the notes, ask how old geocaching is. Students guess, then read: the first cache was hidden on May 3, 2000, the day after GPS became much more accurate for everyone.
  • Pause the hunt after each clue: before Jade and Darius move on, students say where the cache must be and where it can't be, then listen on to check.
  • Run the clue game from the open boxes: a student thinks of a classmate and gives three clues, and the others answer It must be… It can't be… until someone gets it.

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The whole course: English B1.2 · Changemakers

32 lessons for adults at B1 in American English, about people and ideas that changed things: start-ups, future cities, food, memory, customs, art, volunteers and adventure. The podcast team of English B1.1 is back for a season called Changemakers. Learners use the second conditional, the passive, reported speech, the past perfect, relative clauses and verb patterns, and the practice exercises check themselves.See the course

  1. Unit 1 Start-up stories

    the second conditional, If I were you, the first vs the second conditional, also, too, as well and besides

    1. Lesson 1The garage where Silicon Valley beganThe second conditional for imagined situations
    2. Lesson 2Would you sell lemonade to save bees?Second conditional questions and If I were you
    3. Lesson 3Pitch it to the Sharks!First vs second conditional: a real plan or a dream?
    4. Lesson 4A bakery that hires anyone?Adding ideas: also, too, as well, either and besides

  2. Unit 2 Cities of tomorrow

    the passive in the present simple and the past simple, with modals, and in the present perfect and present continuous

    1. Lesson 5Can you cross a city without going outside?The present simple passive
    2. Lesson 6A park on top of a freeway?The past simple passive
    3. Lesson 7Can a desert city catch the rain?The passive with modals
    4. Lesson 8Can an old railroad become a park?The present perfect and present continuous passive

  3. Unit 3 Food for the future

    comparative and superlative adverbs, the future passive, verbs with prepositions, phrasal verbs with up, away and out

    1. Lesson 9Why did Carver tell farmers to plant peanuts?Comparative and superlative adverbs
    2. Lesson 10Lettuce from space?The future passive with will be
    3. Lesson 11Why do corn, beans and squash grow together?Verbs with dependent prepositions
    4. Lesson 12What happens to dining-hall leftovers?Phrasal verbs with up, away and out

  4. Unit 4 Memory and learning

    reported statements with say and tell, tense changes, time and place words, reported questions, requests and commands

    1. Lesson 13Can you train your memory?Reported statements with say and tell
    2. Lesson 14He got better but never rememberedReported statements about the past
    3. Lesson 15Can a TV show teach the alphabet?Reported questions
    4. Lesson 16Can you learn a new skill at 70?Reported requests and commands

  5. Unit 5 Customs and manners

    degree adverbs such as quite and pretty, the past perfect, the past perfect vs the past simple, make vs do

    1. Lesson 17To tip or not to tip?Adverbs of degree before adjectives and adverbs
    2. Lesson 18They'd already started without me!The past perfect: had + past participle
    3. Lesson 19What should you do at a powwow?Past perfect vs past simple
    4. Lesson 20How do you accept a lei?Make vs do: collocations to learn

  6. Unit 6 Art and design

    relative clauses with whose, non-defining relative clauses, relative clauses without a pronoun, when and why

    1. Lesson 21Art that moves in the airRelative clauses with whose
    2. Lesson 22A heart that sells a stateNon-defining relative clauses
    3. Lesson 23What would you paint on a city wall?Relative clauses without who, which or that
    4. Lesson 24Why does the sign say Hollywood?Relative adverbs: when, why and where

  7. Unit 7 Volunteers and changemakers

    verb + -ing or to, -ing as a subject and after prepositions, stop, remember, try and forget, prefer and would rather

    1. Lesson 25A day on, not a day off?Verb + -ing or verb + to
    2. Lesson 26The house that welcomed a neighborhoodGerunds as subjects and after prepositions
    3. Lesson 27A walk that lasted 24 hoursStop, remember, forget and try + to or -ing
    4. Lesson 28Head, heart, hands and healthPrefer, would rather and would prefer

  8. Unit 8 Adventure and challenge

    possessive 's vs of, must and can't for deduction, might, may and could for possibility, the meanings of get

    1. Lesson 29Could you climb a fourteener?Possessive 's, s' or of
    2. Lesson 30 · you're hereIt must be here somewhere!Must and can't for deduction
    3. Lesson 31How did Houdini get out?Might, may and could for possibility
    4. Lesson 32A capital with no road inThe meanings of get

Questions about this lesson

What are modals of deduction?
Modals of deduction are modal verbs for guessing from evidence. Must says you're sure something is true, can't that you're sure it isn't: The arrow points at the bench. It must be under it. The cache stays dry, so it can't be in the pond. The B1 lesson It must be here somewhere! on edio.ai teaches these two on a geocache hunt.
How do you use modals of deduction in the present?
Put the base form after must or can't, with no to and no -s: She must live near here. That can't be Jade. For an action happening right now, use be + -ing: It must be raining. Jade can't be sleeping. The form is the same for every person, and couldn't can replace can't.
What's the difference between must for rules and must for deduction?
A rule says what you have to do: You must sign the logbook. A deduction is a sure guess from clues: It must be under the bench. The negatives split: rules take mustn't (You mustn't put food in a cache), and sure “no” guesses take can't. A quiz in It must be here somewhere!, a B1 lesson on edio.ai, asks which sentence is a rule.
Is it "it mustn't be" or "it can't be"?
For a sure guess that something isn't true, it's it can't be: It can't be in the pond. The short form mustn't is for rules: You mustn't take the cache home. It can be in the pond is wrong here too, because can without not is for things that are sometimes possible. The scheme of It must be here somewhere! lists this mistake first.
What's the difference between must be and might be?
Must be is a guess you're almost sure about, because the clues point one way: He speaks three languages. He must be good at languages. Might be is for something that is only possible. It must be here somewhere! keeps to the sure guesses, and the next lesson of English B1.2 · Changemakers adds might, may and could.
How did geocaching start?
It started on May 3, 2000, near Beavercreek, Oregon, the day after GPS became much more accurate for everyone. A computer consultant, Dave Ulmer, hid a black plastic bucket in the woods and posted its coordinates online. Inside were a logbook, a pencil and prizes; the rule was take something, leave something. Within three days, two people had found it. Today millions of caches are hidden around the world.
How do I teach modals of deduction to B1 students?
Give a clue before every guess, so students see why must or can't fits: Her car isn't there. She can't be at home. Then add must be + -ing for things happening now. It must be here somewhere! on edio.ai goes from episode notes and a park hunt to the scheme, five drills and a chat where every reply rests on a clue.
What's a good game for practicing must and can't?
Try a guess-the-person round: one student gives three clues about a classmate, and the others answer It must be… or It can't be… until someone is right. The open boxes in It must be here somewhere! add more prompts, such as Your phone rings at six in the morning. Who is it?
What's good homework for modals of deduction?
Ask for the best guess from a short situation: The lights in Riley's apartment are off, and her car isn't there leads to She can't be at home. Add sentences to rewrite, such as I'm sure he lives near the park. The ten homework tasks of It must be here somewhere! on edio.ai check themselves, among them a cache page and its logs.
How do you practice modals of deduction one-to-one?
Describe photos and guess together: the teacher shows a picture of a room or a street and asks Who lives here? or What's happening?, and the student answers with must, can't or must be + -ing. The chat in It must be here somewhere! on edio.ai works alone: Estelle reads the clues, and the student picks each guess.
Are there interactive exercises for modals of deduction?
Yes: gap-fills and a clue chat that mark each answer. With no account, this page plays three parts of the B1 lesson It must be here somewhere! on edio.ai: Jade and Darius's hunt in a Kansas City park, a gap-fill with must or can't + the base form, and Estelle's chat that follows the clues. The rest of the lesson is locked.
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