modal verbs

In English, there are the modal verbs: will, would, can, could, shall, should, may, might, and must.

We often use these verbs when there are options or possibilities.


To say the chosen option or possibility. For example, to say what we decide or predict.

Will is useful for saying what we decide or predict for the future.

Would is the past form of will, and is used for the past and in hypothetical situations.

icon showing can - something is an option or possibility Can/Could

To say something is an option or a possibility. (Nothing is stopping it from being one.)


To say something is the right thing to do.


To say there is more than one option or possibility.


To say there is only one reasonable option or possibility.

Remember usage or understand meaning?

Grammar resources often focus on usage, and what modal verbs can be used to express: necessity, possibility, ability, certainty, willingness, obligation, advice, and permission.

But this gets complicated.

Many modals can express the same thing. For example, can, could, and may are common when asking for or giving permission.

And each modal verb can be used to express many different things. For example, can expresses ability, permission or possibility.

It seems random at first. But it’s actually quite logical. When we understand the basic meaning of each modal verb, the uses make sense.

Modal verbs have core meanings

Modal verbs have very simple core meanings.

Each modal verb has a different core meaning relating to how we think about options and possibilities.

The importance of context

The core meaning of each modal verb can express different things in different contexts.

Can in context

Can can express permission, possibility, or ability.

The simple phrase “You can speak English” can express different things. And we understand what the speaker means because of the context.

It can express permission:
“Sorry, I don’t speak much Japanese.”
“That’s OK. You can speak English.” (I give you permission to speak English)

It can express possibility:
“Why are you speaking English in Japanese class? You can speak English at home.” (It is possible for you to speak English at home.)

It can express ability:
“You have many useful skills. You can speak English.” (You are able to speak English)

The basic core meaning of can is: to say something is an option or possibility (nothing is stopping it from being one).
Permission relates to options: The speaker asks or tells someone what is an option for them.
Possibility: Based on our understanding of the world, we can simply say what is a possibility.
Ability relates to both options or possibilities: We understand that something is a possibility and choose to do it.

Must in context

Here are some examples with “must”. The same phrase may express an obligation, make a deduction, or express a requirement.

“Japanese is not accepted here. You must speak English.” (an obligation – you must follow the rule and speak English here, not Japanese.)

“You have lived in the USA for 20 years. You must speak English!” (a deduction – after spending so much time in the USA, it is not possible that they do not speak at least some English.)

“In our office, we use Japanese. However, we have many international clients. So, all staff members must speak English.” (a requirement – Japanese is spoken, but English is also required.)

The basic core meaning of must is: to say something is the only reasonable option or possibility.
Obligation relates to options: The speaker is saying that no other options are reasonable. If this option isn’t chosen, something bad is likely to happen.
Deductions relate to possibilities: There is only one reasonable possibility.
Requirements relates to options and possibilities: Based on our understanding of the world, although other things are possible, (sometimes) this is the only reasonable option.

From this basic core meaning, we can see how different ideas are expressed in different situations.


The system of modal verbs

With Real Grammar, we look at these basic meanings. This helps understand the system of English modal verbs. By understanding context, we can see how modal verbs are used in a variety of situations. But on the other hand, sometimes you can use “can” or “may” (or other modal verbs) to express the same thing.

For example, if I want to ask for some cake, I can say:

“Can I have some cake?”
“Could I have some cake?”
or “May I have some cake?”

So how do you choose?

Many grammar resources say that you should remember may is more polite and can is more casual. But seeing why can help you remember and get a better understanding.

Can is the most direct: “Can I have some cake?”
Can refers to one option. It simply asks: Is this an option, or is something stopping it from being an option?

Could is a little less direct: “Could I have some cake?”
Using could asks the same thing, but uses the past form of can (could). It is not referring to the present situation, but a hypothetical one that is the same as the present, so it is less direct.

May is even less direct. “May I have some cake?”
Using may suggests that there is more than one option: is this one of my options?

And, even “Might I have some cake?” is possible. However, it sounds very formal and is not as common as the other sentences.

So by looking at modal verbs in this way, you can think logically about how they work and even understand nuance. With this understanding you get a better sense of the system of modal verbs and can make better choices when you use English.