How To Teach Modal Verbs With Obligation

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 Probability With Modal Verbs

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 Obligation

Present Tense

Have To / Don’t Have To

In the positive form, it’s used for strong obligation. Usually with this modal form, the obligation comes from an outside source.

“I have to go to bible study on Sundays”

“She has to do her homework for two hours every night”

However, in the negative, it expresses a lack of obligation, or none at all.

“I don’t have to go to class today”

“My husband said that he doesn’t have to work on Friday, so we’re going to the beach”

Must / Mustn’t

In the positive form, ‘Must’ indicates strong obligation, often from the speaker themselves. In the negative form it can be the same, but is also used for outside sources.

“I must do some more painting today, I was too busy last week”

“I mustn’t watch that show any more, it just upsets me”

“You mustn’t use your skateboards here”

Should / Shouldn’t

This is less strong than the other two and is often used for mild obligation and frequently for advice or suggestion.

“You should start doing some more exercise if you want to lose weight”

“You shouldn’t talk about other people in that way, it’s not kind”

Be Careful! Watch out for the difference between ‘Mustn’t’ and ‘Don’t Have To’. The former means that it’s forbidden, whereas the latter indicates something that you can do, but don’t need to do if you don’t want to.

Past Tense

Had To / Didn’t Have To

Just as in the present tense, the positive form indicates strong obligation, whereas the negative means simply that there is no obligation.

“I had to clean the whole car to get the smell out”

I told my mother that I didn’t have to go to summer school”

Should Have + Past P / Shouldn’t Have + Past P

In the positive and negative forms, this one is for a past action which the speaker regrets or feels should have happened differently, or for advice that wasn’t followed.

“You should have asked me before you went to play with your friends”

“He shouldn’t have lied, it made everything worse”

Be Careful! It is possible to use ‘Must’ in the past (Must + Have + Past P) But we use it to express speculative statements or probability. Students shouldn’t use it to mean strong obligation in the past, for this we have ‘Had To’, for example;

“Rosie hasn’t landed yet, the flight must have been delayed”

Any more questions about Modals with Obligation? Let me know in the comment section!

Happy Teaching!




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