Speculating about the past is one of the few grammar points I have not covered yet. As I usually teach lower level students, and this grammar is for intermediate students, I haven´t felt it necessary to deal with it. However, now the time has come and I need this explanation for one of my students. I hope you will profit from it too.
In this post, there are two infographics explaining the grammar and usage of these constructions. Then, there is a worksheet where students can practise the grammar they learn.
Modals and perfect infinitive – infographic
Explain, that we need to say who + modal + perfect infinitive to speculate about the past. Then show the second infographic and explain the meaning of the modal verbs with the perfect infinitive.
Now that your students know how to form the speculations and what is their meaning, I would ask them to take their exercise books and use the phrases from the infographics and write as many sentences as they can in 5 minutes. In this way, they will practise forming the speculations.
Speculating about the past – worksheet
In the first exercise, students match the sentences with the same meaning. The correct solution is: A3, B2, C6, D5, E4, F1.
In the second exercise, students practise forming the speculations. They have to write the whole sentences this time. The correct solution is: A) Shakespeare might have written this play. B) She must have stolen the money. C) She can´t have driven that car. D) Mark must have spoken to her. E) David can´t have read the book. F) He may have lied.
In the last exercise, students complete the sentences with the correct combination of the modal verbs and perfect infinitives. They use the verbs in the brackets. The correct solution is: 1. must have worked 2. might have forgotten, can´t have got 3. can´t have seen, may have seen, must/might have mistaken 4. can´t have got, must have drunk 5. might have come, can´t have come, might/could have given, could/might have come.