How To Teach Probability With Modal Verbs

Most of the time, modal verbs do not have an exact or sometimes not even close translation in a student’s mother tongue. They can therefore be difficult to teach. Have a look at this guide when you need to teach meanings, form and use so that you always have the answers to those pesky questions!

What is a Modal Verb?

Well, technically a modal verb is a verb that doesn’t have an infinitive or a past tense. But it’s also a type of auxiliary verb used so that we can effectively express modality, by which I mean probability, obligation, permission and ability. This post is for all things probability, see my other posts for the others.

How To Teach Modal Verbs With Obligation

The form is very simple, a modal verb is always followed by a bare infinitive (without the ‘to’). There is one exception to this, which is ‘ought’. ‘Ought’ is followed by the ‘to’ infinitive’.

Modals To Express Probability

Present Tense

Might / May / Could

“She might be able to help you”

“He could have what you are looking for”

“I may be able to come to the party, but I have to check my calender first”

These three are for something that you are not sure about, as seen in the examples above. For all intents and purposes, they are exactly the same.

Must / Can’t

If we are almost completely sure about something, we use the following;

Must – “She must be at work, I can’t get hold of her at home”

Can’t – “He can’t be on holiday, I saw him this morning”

Be Careful! Notice that we use ‘can’t’ for the negative form. It is not possible to use ‘mustn’t’ in the same context, as it doesn’t have the same meaning. See below!

Should / Shouldn’t

We use ‘should’ to make a supposition about something which is probably true, if everything is as we expect it to be. Or according to facts that we have.

“We should get our food soon, we’ve been waiting ages”

“It shouldn’t take long for the builders to finish the extension”

Will / Won’t

If we are very sure about something we use these two.

“She will be in Greece by now”

“She won’t realise until she gets to Greece that she has left her phone in my car”


Finally, we use ‘can’ to talk about general possibility.

“It can rain heavily at this time of year”

Be Careful! We don’t use it for specific possibility, for that we use ‘could’.

Past Tense

Like I mentioned before, a modal verb doesn’t have a past tense, so you have to add ‘have’ to express the same idea in the past. But remember the golden rule, a modal verb is always followed by the infinitive, which means that you have to always use ‘have’ and not change it to ‘has’ or any other form.

Also, lets not forget that ‘have’, being an auxiliary verb, is always followed by the past participle.

Might / May / Could + Have + Past Participle

Just like in the presen tense, these have exactly the same meaning. For when you’re not sure about something.

“She might have missed the bus, I haven’t heard from her”

“I could have dropped it on the way here”

“He may have decided not to go ahead with the procedure”

Must / Can’t + Have + Infinitive

Again, these are for complete or almost complete certainty.

“She must have read the article because she quotes it all the time”

“I can’t have lost it, I had it a moment ago!”

Should + Have + Past Participle

Used for something we think has happened, based on information that we expect to be true.

“She should have left the office by now, she’ll be here soon”

Will / Won’t + Have + Past Participle

For past certainty, similar to the meanings of ‘Must have’ and ‘Can’t have’. Something that we are completely, or almost completely, sure about.

“She will have arrived at the office by now, she left the house half an hour ago”

“The letter won’t have arrived yet, I only sent it yesterday”

Could + Bare Infinitive

‘Could’ in the past doesn’t require the auxiliary verb and the past participle if it’s used to express general possibility.

“She could be bad tempered at times when was little”

Be Careful! It is not used to talk about specific past possibility, for this we use ‘Could + Have + Past Participle’.

Any more questions about probability? Let me know in the comment section!











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