Modal verbs | The parts of speech | Grammar | Khan Academy

Hello grammarians! Today we're going to talk about a class of auxiliary or helper verbs called the modal verbs. These are verbs that have special properties and help other verbs. But what is modality? My fellow grammarian, I am so glad you asked!

Modality is when we use these verbs to express conditions on stuff. So we can use these verbs to determine if something is likely to happen or certain to have happened, whether or not something is possible, or whether or not we have the ability to do something, whether or not we have the permission to do something, and whether or not we have the obligation, requirement, or need to do something. You already know all of these verbs; I promise you, you just didn't know this name for them.

Let's meet the modals! Roll call, here we go: may, might, must, can, could, shall, should, will, would. Those are the modals!

So here's what modal verbs can do. Thing number one: they agree with everything. You can take any one of these modals and you can use any subject in the world, and it's not going to change, right? You take a word like "talk," for instance, and you'd say, "I talk," "Diane talks," right? You add the "s," but any subject in any sentence is going to take the modal verb the same way.

Let me show you: I can do it. You can do it. She can do it. They can do it. We can do it. It's all the same! They agree with everything.

Something else that modals do is actually something that they don't do: they don't have a "to" form. This is what we call the infinitive. So there's no such thing as "to may" or "to could." That just doesn't exist! So modals don't have infinitives. You can't say, "I want to should." It doesn't; that is an illegal operation in English. It is ungrammatical. It doesn't matter what version of English you speak; across all varieties of English, you cannot "to should."

And finally, a thing that modal verbs can do is indicate modality, which, like we said, establishes conditions. So let's take a look at some examples.

So the word "must," right? We can use the word "must" in a couple of different ways. So if you imagine a detective looking up from some tracks, some muddy boot prints on the floor with her magnifying glass, she looks up and she says, "He must have gone that way." That detective is saying, using "must" to express a likelihood, a high likelihood; this must have happened.

But if you're at an amusement park and the roller coaster you want to ride has a height requirement, the sign probably says, "You must be this tall to ride the Doom Coaster." This is like a necessary condition. By a similar token, if you enter someone's house and they demand that you take off your shoes, they would say, "You must remove your shoes."

Similarly, with "may," we can use "may" to express a possibility, like saying, "It may rain." That's something that could possibly happen, or to give someone permission, like "You may enter."

You can use a word like "can" to express ability. You could say, "I can eat 10 pounds of broccoli," and that's expressing your ability to do a thing. We also use modal verbs like this to talk about conditions or stuff that isn't going to happen or maybe could happen.

Uh, and so for example, in this sentence we would say, "I would make the bed but I'm tired," because the possibility exists, however remote, that the bed would be made by me. But I don't feel like it, so I'm using "would" to offer an excuse. I'm saying this could possibly happen; this would happen except for this one other problem, which is that I'm sleepy.

You can also use modal verbs to give advice to someone, as in "You shouldn't do that." And something that is special to "will" and to a lesser extent "shall" is that they can form the future. "Shall" used to be a lot more popular, and it still is in British English, but less so in standard American. So you would say, "He will win the competition" or "He shall win the competition."

The use of this modal verb "will" or "shall" indicates that that thing that you're talking about is happening in the future. These verbs are very powerful. You should learn how to use them, and in fact, if you can complete the exercises, then you will master these tricky verbs. You can learn anything.

Dave it out!