Here’s a quick exercise to introduce the topic of using modal verbs to express speculation and deduction. The key objective is to activate previous knowledge, which may or may not have been formally taught.
At the beginning of the session, show the students the picture above, and give them a couple of minutes to think of sentences about it in pairs. Then have the students share their sentences with the rest of the class. You should write their sentences on the board, reformulating if necessary.
Organise their answers so that factual statements are on the left-hand side of the board, and any speculative sentences are on the right, but at this stage don’t explain this division. If your students run out of ideas for this picture, show them others, such as the one on the right. You can find other pictures here.
Once you have a good selection of sentences on the board, ask the class why you have organised their answers on the board as you have. Depending on the previou knowledge of the class, you may have some sentences which use modal verbs correctly, and you can use these as a base for reviewing the necessary structures. In any case, you have sentences which have been created by the students to serve as model sentences, which makes the lesson more personal and so more significant for them.
As a follow-up exercise, I ask students to find and bring to class photos of interesting-looking people . I mount these on cards on the wall, then students write speculative sentences on post-its or on slips of paper and stick them around each photo. For this activity, it’s best to avoid photos of famous people. Adverts in magazines can be a good source of pictures. Here’s one which would work well (although it’s not a photo).