Short answer
Give learners a fictional mystery and a set of clues, then ask them to discuss what might, could or must have happened. In S06E13, Gav and Em use the evidence to practise past-modal deductions while deciding which explanations are possible.
Pre-teach or display the forms learners need, and prompt them to restate an idea if they use the wrong tense. Keep the activity open enough for several theories, and let new clues change the group’s thinking.
Try this in your next lesson
Use our staged clues and worked answers below to contrast present and past deductions. Ask what supports each conclusion and whether another explanation is possible.
👇 Scroll down for our practical checklist or activity and download.
Listen to the whole S06E13 discussion in our podcast episode guide here🔊.
Introduce the situation and language
Set a clear fictional context, identify the people involved and give learners a few clues. Review forms such as “might have”, “could have” and “must have” before the discussion if the class needs support.
Ask learners to explain their theories
A missing object, an open window or a clue left behind can lead to several possible explanations. Encourage learners to distinguish what they know from what they are guessing, and support them in phrasing a deduction.
Keep the conclusion open
Do not reveal a single solution too early. The episode’s demonstration is playful and leaves many clues still to discuss. In a class, the reasoning and language practice can matter more than reaching one answer.
Make certainty part of the language task
For past deductions, model modal + have + past participle: Someone might have opened the window. Must have expresses a confident deduction, while might have or could have leaves a possibility open. A clue is not automatically proof. Ask what else could explain it before treating one theory as certain.
Our new classroom scenario can use a missing trophy instead of a death if that suits the group better. A window is open, the trophy is gone and a caretaker moved some boxes. Learners suggest explanations, then learn that the trophy has been taken away for cleaning. There is no need for one winning detective. Ask learners to explain which earlier theories remain possible and why they would change the strength of a claim.
Gav and Em suggest: present or past, possible or certain?
Our original B1–B2 classroom extension. The fictional projector and trophy clues below are new teaching material, not further events from the podcast mystery.
Keep time and certainty separate
Present: modal + base form: “It might be in the cupboard.” For an action in progress, use modal + be + -ing: “They might be moving it now.”
Past: modal + have + past participle (verb 3): “Someone might have moved it.” Keep have after the modal, including with he/she: “She must have moved it.”
For this deduction task, must expresses a conclusion the speaker feels sure about; might/may/could leaves a possibility open; can’t rules something out with confidence. Past forms include must have, might/may/could have and can’t/couldn’t have. Evidence may change the conclusion; these are not fixed percentage labels.
Important contrast: “It can’t be there” means we feel sure it is not there. “It might not be there” leaves its absence possible. Teach can’t as the negative counterpart to deductive must here, rather than mechanically changing must to mustn’t. In “You mustn’t move it”, mustn’t expresses prohibition.
Give the clues in stages
Tell pairs: “A projector has been moved from a shelf into one of three cupboards: red, blue or green. It remains in one of them.” Reveal only one stage at a time.
Stage 1: The red cupboard has just been checked and is empty. Blue and green have not been checked.
Possible answers: “It can’t be in the red cupboard.” “It might be in the blue cupboard.” “It could be in the green cupboard.” Ask which clue supports each claim. The evidence does not yet justify “It must be in blue”.
Stage 2: The green cupboard is checked and is also empty.
Possible answer: “It must be in the blue cupboard.” This conclusion depends on the stated rule that it is still in one of those three cupboards. Without that rule, another location remains possible.
Look back at what happened
Now add: “The projector was on the shelf at nine and was moved by ten. A was away from the building throughout that hour and could not physically reach it.”
Models: “Someone must have moved it off the shelf.” “A can’t have moved it personally during that hour.” Ask learners to contrast “It must be in blue” with “Someone must have moved it”: the first concerns its location now; the second concerns an earlier action. We still do not know who moved it. Do not turn an unknown person into a certain culprit.
Try fresh clues and check the reasoning
Use a trophy instead. It is still in one of two rooms, the hall or the office. The hall is checked and empty. The trophy was on its usual shelf yesterday but is missing from it now. No information identifies the person who moved it. Ask each learner for a present conclusion, a past conclusion and a possible explanation.
Answer guidance: “It must be in the office”; “Someone must have moved it from the shelf”; “A cleaner might have moved it.” The cleaner is only one invented possibility, not an established fact. Accept other plausible explanations with appropriately cautious wording.
In pairs, one learner proposes and the other asks “What makes you think that?” Then swap. One-to-one, we take the partner role; online, reveal each clue separately in chat. Listen for time reference, form and strength of claim. If the learner says “must moved”, cue “must have + verb 3”; if certainty is too strong, return to the clue and ask what else remains possible. Give a fresh attempt after feedback.
Grammar references: British Council present deductions and past deductions. The PDF below is the original short mystery practice card; this expanded sequence and answers are supplied on the page.
📥 Download the free teacher practice card (PDF)
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