What is the most appropiate modal verb in this context?

Question

I had an English exam where I had to choose the most appropriate modal verb. The sentence was like this:

Although he is an obedient student, he ____ be disobedient at times.

So, I chose ‘may’ by assuming the person has the possibility to be a menace. However, my English teacher considered it as the least appropriate one and tried to convenience me that the verb ‘can’ is the best choice as it reflects the person’s ability rather than possibility.

Therefore, I was wondering if my teacher's statement is true from both a native’s perspective and a grammarian’s perspective.

Answer 1

I would have chosen "can". This is the most idiomatic, but it has little to do with logic, or the meaning of "be able".

The reason is subtle and seems to be connected to the fact that a person has a free will to choose to be disobedient. Modals like "might", "may" or "will" assume that disobedience is a the result of some automatic or random system, something that is out of the control of the individual.

He will be disobedient. -> A certain prediction, there is nothing that he can do to prevent it.

He may be disobedient -> There is a random chance of disobedience, again this suggests that he has no control.

He can be disobedient -> He will be disobedient only if he chooses to be disobedient.

Using "can" like this is personifying, it makes an inanimate thing seem to act like a human.

This computer program can crash sometimes. (Suggests that the computer is like a person and crashes when it chooses to)

Your posted picture is irrelevant, since it doesn't deal with people choosing to be difficult but is examples of the idiomic "it may be difficult (to do something)"

Answer 2

Although your choice of may is grammatically correct, the idiomatic answer is can.

We tend to say things like: He can be awkward / difficult / challenging after "although" introductions that weigh dubious behaviour against some desirable quality**.

Although he's bright, he can be lazy if not pushed.

After a different introduction such as: Be careful with that horse, he may buck, the use of may is more appropriate.

This is really a question about how native English speakers talk rather than grammar. It's a test of your familiarity with the idiom.

Answer 3

The simplest context to imagine for that sentence is no context, where someone is simply describing a student. If that's the case, then "can" is correct because it means he has the potential to be disobedient at times. "May" would mean contradictory things: he's obedient, but maybe he's disobedient at times. The first statement claims enough knowledge of the student to make an assessment, while the second claims insufficient knowledge to make the same assessment.

On the other hand, if the context is a teacher handing off a class to another teacher, both are correct, but "may" would make more sense because it has a predictive meaning, along the lines of, he's generally obedient, but he may disobey you at times.