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  • - [Voiceover] Hello grammarians!

  • Today we're gonna 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

  • or 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.

  • So you can take any one of these modals

  • and you can use any subject in the world

  • and it's not gonna change, right?

  • You take a word like talk, for instance,

  • and you would 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.

  • 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 different ways.

  • So, if you imagine a detective looking up from some

  • tracks, some muddy bootprints on the floor,

  • with her magnifying glass.

  • She looks up and she says "He must have gone that way!"

  • That detective is 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 ten 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.

  • 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 would say "He will win the competition."

  • Or "He shall win the competition."

  • And 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.

  • David out.

- [Voiceover] Hello grammarians!

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

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    Cai Xin Liu posted on 2016/08/20
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