Teaching the difference between can, may, and must is challenging because these words have different meanings depending on the context in which they are used.
Use of Can, May and Must
“Can” is used to express an ability to be able to do something, to ask for permission, and to make requests or suggestions. “Could” is the past form of “can” and is used to describe an ability that someone had in the past, to express permission politely, or to express possibility.
“May” is also used to suggest that something is possible and is used to ask for formal permission. “Might” is the past form of “may” and used to suggest a smaller possibility than “may”.
“Must” is used to express something important, formally required or necessary, and to show that something is very likely.
My lesson teaching the distinction between these words begins with the question “Can you drive a car?” and the warm-up exercise requires the students to look at some pictures of people skiing, cycling, playing the piano and playing badminton to ask “What can they do?” This makes the students aware of the connection between “can” and a learned skill or ability. I then use pictures to demonstrate that “you cannot” or “you can’t” is less strict and less formal than “you may not” giving examples such as “you may not smoke” and “you can’t eat and talk at the same time.”
Next, I introduce the idea that “may” also means that something could happen, using pictures that show that it may rain, he may win the race, and the shark may eat a swimmer! Using “must” to express the idea that a specific action is important comes next, with examples including “you must do your homework” and “you must not walk on thin ice.”
Taking a Driving Test
The students then guess the missing can/may/must words from a dialogue about learning to drive, which they then practice in pairs. This short exercise leads to the main activity, taking a driving test! Since these auxiliary words are used to express different forms of permission, using road signs is an effective way to teach the distinctions between the relative strength of the words. Usually, road signs express these distinctions very clearly. Let’s take UK’s road signs for examples.
- Circular red signs give strict orders for road users and can be expressed in the form “you may not”, such as “you may not turn right”.
- Circular blue signs give orders, such as “you must turn left”.
- Triangular red signs give warnings and are useful for expressing possibilities such as the road may have queues or wild animals.
Following a short review of can, may, and must using road signs as a visual aid, one student from each team is blindfolded and their team has to direct them around a simple obstacle course in the classroom using the three words correctly. This game has to be managed carefully to keep the student’ safe but is a really great way to engage students whose physical learning style is dominant.
Create Prison Rules
Another place where people’s behavior is closely controlled is in prison, and the next activity requires the students to create 10 prison rules using the three words correctly for the team, or student, who failed the “driving test” in the main activity. This then leads to another dialogue where one student plays a prison counselor interviewing the prisoner about how they “drove” themselves (around the classroom!) without a license, and ended up in prison, and what they can learn from this mistake. The next advanced activity requires the students to swap roles and use their initiative to create a new dialogue, where the counselor gives advice to the prisoner using can/may/must in response to different scenarios, such as wanting to finish school, but being unable to, because they are in prison.
Creating Silly Rules for the Imaginary School
Schools also have lots of prescriptive rules and another activity begins with me drawing a picture of the school on the board. I then ask the students to create silly rules for the imaginary school. The students then take it in turns to draw visual representations of the rules, or what may happen as a result of the rules, on the board, for the other students to guess the rule. The winning student has to write the rule on the board in good English before they draw another situation for the class to guess, but if they fail to use can/may/must correctly, they forfeit their chance to draw on the board. When the board is full of rules and crazy situations, the students then create a dialogue where they describe the school to their parents. Advanced students can use this opportunity to compare the relative strengths and weaknesses of the real-life rules with the crazy rules they created, and explain the reasons why they consider which school is best.