Past tense of modal verbs

The past tenses of the modal verbs MUST, CAN and CAN’T often cause problems, even for advanced students of English. I have heard some of my best students, who had already passed the CAE exam, use words like MUSTED, and I was not happy about it. That is why I try to teach this grammar thoroughly.
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[showmyads] In this post I would like to share an infographic and additional exercises I use to teach this grammar point. I hope you find this post useful. Please don’t hesitate to share any of your materials on this topic. You can send them to my email: rotreklzdenek @gmail.com. Thank you.

Display the following infographic to your students and explain that MUST does not have a past tense. Instead, they should use the past tense of HAVE TO. Go through all the verbs and elicit their meaning. Then ask your students to work in pairs. One of them will turn with their back to the screen, and the other will say the verb in the present tense. The student whose back is turned then has to say the verb in the past tense. It is a kind of drill, but if you ask your students to do this for one minute each, it is very effective.

The following quiz is in HTML 5 so it will work on all mobile devices and desktop computers. Students can do the quiz either at home or at school in a computer lab. If they complete each of the texts with the correct modal verb in the past tense they will be rewarded with a game.

Modal verbs in the past tense quiz

There are some very interesting exercises at the British Council site.
There are more exercises on this topic at the BBC learning English site.