HAVE TO vs MUST: Learn the difference between these two modal verbs (English grammar lesson)

Hello.

This is Jack from ToFluency.com and in this episode of Ask Jack, I’m going to talk about

2 common modal verbs and the difference between them.

Marie asks, “What’s the difference between ‘must’ and ‘have to’?”

Thank you for this question.

Now, this is a very complex topic and it’s not always easy to explain the subtle differences

between these 2 modal verbs.

You know, especially when they’re so common and they have different meanings and they’re

used in different ways depending where you live.

And, I don’t want to confuse you.

You know, in order to really understand how to use these 2 modal verbs, it’s important

to get that input, you know, something I talk about all the time.

But, I will highlight a few things that are going to help you when it comes to using these

2 verbs.

Firstly, both of these verbs, both of these modal verbs can be used for obligation.

You know, I must decorate the Christmas tree.

You can’t see this but there’s a giant Christmas tree here and I must decorate this

soon or I have to decorate the Christmas tree soon.

Now, the difference and I think this is specific to British English.

It might be used in different countries too but I know it’s not as common in American

English, okay.

There’s a subtle difference between I must decorate the tree and I have to decorate the

tree.

When I say ‘I must decorate the tree’, this is an internal obligation.

It’s something that I’m saying that I must do.

It’s coming from inside.

I must decorate the tree soon.

However, my wife says to me, “Jack, let’s do this tonight.

We have to do it tonight.”

This is more of an external obligation because my wife is telling me I have to do it.

So, I can tell my friends who say, “Jack, let’s play poker tonight.

Okay, let’s play some poker tonight.”

And I say, “I can’t because I have to decorate the tree.

I have to decorate the tree tonight.”

Now, if you’re a little bit confused, I’m talking about a Christmas tree here.

You know, I’m filming this in December.

So, I have to decorate the Christmas tree tonight.

It’s an external obligation.

My wife is telling me I have to do it.

The example for this that is used all the time is the doctor, you know, and you say,

“I have to take these pills every day for 2 weeks.

It’s an external obligation.

The doctor’s telling you, “You have to do this.”

An internal obligation, another example, “I must study harder.”

I must study harder.

That’s an internal obligation where it’s you that’s deciding on this obligation.

When we’re talking about obligation in the negative form, we can’t use have to because

if I say, “You don’t have to do your homework”, it means it’s not necessary.

There is no obligation.

You can but you don’t have to.

It’s up to you.

And, a lot of people feel that or a lot of people think when you say “You don’t have

to do it” that it’s the obligation but in the negative sense.

It’s not.

As I say, it’s saying that it’s not necessary.

You can do it but you don’t have to do it.

Okay, so when we’re talking about obligation in the negative, generally, we say, “You

can’t do that” or “You mustn’t do that.”

Now, we use mustn’t in this sense again.

But, that’s a big different to know.

You don’t have to do it.

Just think about, you know, when you are at school, you know, or when you were at school

and the teacher said “You have to do your homework”, you don’t have to do all of

these exercises but you have to do some homework.

You don’t have to study before the exam, but you should.

So, it’s, you know, when we’re using “You don’t have to”, it’s you can if you

want to but it’s not necessary.

One last thing I want to say about must because there’s another way that we can use it.

We can use it for certainty, when we are sure about something, okay.

Now, just look at my hair.

In my live lessons, a lot of people comment on my hair so it’s a topic of discussion.

And, someone might say, you must be wearing hair gel” or “You must have gel in your

hair, you must have gel in your hair” because they are certain I have gel in my hair because

of the way it looks.

Okay, another example is my friend arrives here, okay.

He arrives and he says ‘I have been traveling for 16 hours now.

I’ve been in the car for 16 hours.”

I say, “You must be exhausted.”

So, it’s when you are certain about something.

Okay, you must be exhausted and we use it when we’re basing our prediction, you know

our certainty on other factors.

You know, something that we can evidence, you know, some kind of evidence.

My hair is the evidence, “You must have hair gel in your hair” and my friend who

says he has been driving for 16 hours, “You must be exhausted.”

So, hopefully, that has given you an introduction to the difference between must and have to.

As I say, you know, there are lots of different exceptions and different things going on here

but that is the general idea of how to use these 2 words.

In the comments section, what I want you to do is to just give me some examples of these

2 modal verbs.

Talk about a context, maybe do a dialogue but give me some examples in the comments

section and I will comment on those for you.

So, thank you for watching this video and I’ll see you next time.