While most students are able to explain what most verbs do, such as convey action, movement or behaviour, modal verbs might seem more mysterious. Modal verbs are a specific set of verb which convey an attitude or mood. They include can, could, will, would, may, might, must, shall, should and ought. When explaining modal verbs, you need to build upon the knowledge that students already have. This will allow them to acquire a well-rounded and comprehensive understanding of these verbs in order to use them correctly.
State three different sentences using modal verbs to the class. For example, "I would go to the party, but I'm too tired," or, "I can play piano," or, "I should call my doctor." As you can see, it is easy to think of examples that use modal verbs since they are words we are all familiar with and use constantly.
Elicit from the class what all these sentences have in common, in terms of the tone or intention of the speaker. Your students should identify that all the sentences contain sentiments about attitudes or moods. You can now point out that all the sentences contain modal verbs.
Write all 10 modal verbs on the board. Explain that they all have many different uses. Point to each verb, and ask students to use it in a sentence. Ask students to keep coming up with a sentence for each verb, until you've covered the several usages of each modal verb together as a class. For example, for the modal verb "can", students might think of the usage for skill and ability immediately (such as "I can play tennis") as well as permission ("Can I go to the bathroom?") but you may have to add usages such as the one for privilege ("The President can veto that bill").
Give students a worksheet which has at least 10 sentences with misused modal verbs. Ask students to read each sentence and make the appropriate correction themselves. Go over the worksheet together as a class. This will showcase to you how much your students understand.