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.