How to Teach Modals of Possibility/Probability/Deduction

Alex Case
Short but thorough guide to teaching “must have done”, “can’t be”, etc.

Modals like “It must have been the CIA” and “It can’t really be Elvis!” are so much fun that many teachers already spend too much classroom time on this point. However, that doesn’t mean that this grammar point is necessarily well taught, and many classes could benefit from more emphasis on typical student confusions, pronunciation and related forms before moving on to classic activities like guessing ambiguous pictures. The practice stage could also be made more useful by adding less controlled and so therefore at least slightly more realistic speaking tasks.

Typical student confusions when studying and using these kinds of modals include:

  • Trying to use “can” as the opposite of “can’t” and/or “mustn’t” as the opposite of “must”, perhaps because those are the opposites when the verbs have different meanings (e.g. “I can ride a bike”/“I can’t ride a bike”)
  • Thinking “could” and “might” must have past meanings
  • Confusions between “must” and “will”
  • Trying to use “be” in all sentences (often because the form is taught as “must have been” etc rather than “must + have + PP”)
  • Trying to use “should” and “would” in context where it isn’t possible

“Should” does actually have this meaning, as indeed do all true modals, but it is much more limited in use. In most practice activities “That should be some kind of bird” and “Aliens should have landed here” would be wrong, so it is usually best to ignore this form. This leaves, in approximate order of certainty:

  • must
  • may/might
  • could
  • can’t

I’ve seen quite a few lists that put “could” higher than “might/may” but I would argue that “It cooooooould” with extreme intonation to show more doubt is more common than “It miiiiiiiight” and “It maaaaaaaay”. Varying the level of certainty in this way is a pronunciation point which is well worth teaching, and something that means it is usually best to avoid putting percentages on each verb as some books do.

You can also show the level of “could” with a look at the useful area of collocations with these verbs. I would also argue that “could possibly” is a more natural collocation than “might possibly” and “may possibly”, with the more certain “might well” and “may well” being more natural than “could well”. The collocations “really must” and “really can’t” are also worth teaching.

A fuller list with variations of pronunciation and collocations could include:

  • really must
  • must
  • may well/might well
  • may/might
  • could
  • could possibly
  • coooooould poooooossibly
  • can’t
  • really can’t

I often get students to put such expressions into a graded list in just this way as a discovery approach to presenting the language, with example sentences spoken by the teacher or on a CD helping them use the doubtful or sure intonation to check their answers. Lower-level classes might not need all the collocations, but I do “cooooould” with all classes and “REALLY MUST” with most as a way into the very important pronunciation point. All classes also get additional expressions which are not modal verbs but are always needed for communicative activities that get students to make deductions. All my classes get “probably”, as it fills a vital gap between “may/might” and “must”. Most also get “almost certainly”, with the negative forms “probably not” and “almost certainly not” also being useful. Higher-level classes also get “will” to give me a chance to clear up the confusion that both “must” and “will” basically mean 100%, but with the former being according to my logic and the latter seen as a fact. To help with this, after they try to put the expressions into order I sometimes give classes a ranking sheet with hints like this:


2. It’s a fact.

3. I’M SURE!

4. I’m sure.

with the answers being “will definitely”, “will”, “REALLY MUST” and “must”.

As well as presenting modals as part of a general lesson on speculating, you can also do so as part of a lesson on hedging/generalising, e.g. giving students statements like “TV has no future” to make it more realistic.

Higher-level classes might also benefit from a whole lesson on different grammar of modal verbs depending on their meaning, e.g. that “couldn’t” is the past of “I can’t speak Spanish” but “can’t have been” is the past of “It can’t be the right thing to do”.

Practising modals of possibility/probability/deduction

FCE Speaking tasks with pictures, especially Speaking Part Two, are really good for this point. In that task, students compare two pictures that they’ve never seen before and therefore need to say things like “This could be a lake too, but it’s probably the sea”. To emphasise this language point, you can get them to speculate on one picture before you show them the second one to compare with it. Another way of doing that is to give two groups one of the two photos each to speculate on, then put them in pairs to find the similarities and differences without showing the pictures to each other, insisting on speculating language at that stage too.

It’s also possible to make discussion questions similar to FCE Speaking Parts One and Four (and the similar IELTS Speaking Parts One and Three) such as “Who was your favourite teacher at school? Do you think they enjoyed their job?” and “What are your predictions for the future of this city?”

Written by Alex Case for EnglishClub
Alex Case is the author of TEFLtastic blog.

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