Today we're going to look at two modal verbs and a semi-modal verb that are often

confused with each other.

These are: should,

must and have to.

We'll have a brief look at their formulation and then we'll look at their

usage and differences. And. we'll finish this lesson with a gap filling exercise. By the end of

this video, you should have a good idea of the differences between these three verbs.

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So when you're ready,

we can begin our lesson on 'should', 'must' and 'have to'.

Modal verbs:

'should, 'must' and 'have to'.

Let's look at formulation first.

'Should' and 'must' are real modal verbs

and therefore,

like all modal verbs,

they're always followed by the 'infinitive without to'.

"Should do", "Must do".

And, they're the same for all the pronouns.

"I should", "He Should", "It Should" etc.

Also,

they do not need auxiliaries;

they take direct negative and question forms:

"I shouldn't.",

"We mustn't.",

"Should I?",

"Must we?"

And finally, they never combine with another modal verb.

You can't say: "you should can". You have to replace 'can' with an alternative:

"You should be able to..." Or

instead of "He will must".

You'll have to say:

"He will have to".

'Have to' is a semi-modal verb.

It is like a modal verb because it fulfils a specific function,

but it behaves like an ordinary verb in its formulation.

It is followed by the 'infinitive without to'

"have to do",

but it is conjugated according to pronouns:

"I have to",

"He has to" etc.

It needs auxiliaries.

It doesn't take direct negative and question forms.

"I don't have to."

"She doesn't have to."

"Do I have to?"

"Does she have to?"

And finally, it can combine with modal verbs:

"You will have to."

"He might have to."

Right then,

let's have a look at usage,

starting with should.

The first use of should is expressing an opinion

or giving or asking for advice.

Let's look at some examples.

"I believe nurses should have higher salaries."

"You look tired.

I think you should have some rest."

"He shouldn't make a rushed decision."

"Do you think we should phone her?"

"What should I say when I speak to him?"

The second usage of should is expressing an expectation.

For example:

"He should arrive any minute."

"He shouldn't be long now."

"He should have arrived by now."

And the third usage of should is expressing regret about a past action.

For example:

"You should have been more careful."

"I shouldn't have said that."

'Ought to' is a synonym for 'should'.

It generally sounds more formal than 'should',

and is less commonly used,

particularly in the question form:

So you could say:

"You ought to have some rest."

"He oughtn't to make a rushed decision."

"I oughtn't to have said that."

But it would be uncommon to say

"Ought we to phone her?"

Also 'should'

(but not 'ought to')

is used to express a small possibility.

For example:

"If I should ever go back there, I will not make the same mistake again."

Or

"Should you need any further assistance,

do not hesitate to contact me."

This is a common formula in formal writing.

Right then, let's move on to 'must'.

The first usage is expressing a necessity

felt by the speaker.

We use 'must' for the present and future tenses.

For example:

"He is very ill.

You must call a doctor now."

"We must not lose the match tomorrow,

or we will be out of the tournament."

"This is the best book I've ever read.

You must read it too."

"You mustn't hesitate to call me if you need help."

Looking at the second usage of 'must'.

It expresses a prohibition.

Once again in the present or future tenses.

"You must not use your mobile devices during take-off."

"You must not be late for your interview tomorrow."

And the third usage of must is an assumption in the present or past

in affirmative sentences only.

For example:

"You must be tired after your very long day."

"He must have read my letter,

because he repeated exactly what I had written."

Okay let's have a look at 'have to'.

'Have to' expresses an external obligation

in positive sentences.

For example:

"You have to make an appointment to see him."

"She has failed her exam.

She has to retake it."

The second usage is expressing a necessity or obligation in the past.

"He was very ill. We had to call the doctor immediately."

"He was very busy.

I had to make an appointment to see him."

Finally, 'have to' removes a necessity or an obligation

in all the tenses, present, past and future.

"He feels much better now.

You don't have to call a doctor."

"I didn't have to make an appointment to see him."

"She has passed her exam.

She won't have to retake it."

So as you can see,

the main difference between 'must' and 'have to'

is that 'must' is a necessity felt by the speaker,

whereas 'have to' is an external obligation or rule.

If this difference is not relevant

you can use 'must' and 'have to' interchangeably

in positive sentences.

However, be careful

that in the negative,

'must not' is still a necessity

or an obligation

not to do something.

It's a prohibition.

Whereas 'don't have to'

removes the necessity or obligation.

Also note that as 'must' has no past tense

both obligation and necessity are expressed with

'had to' to in the past.

You may have also come across

the expression 'need to'.

'Need to' is a softer alternative to both 'must' and 'have to'.

For example:

you could say, "I must finish this tonight, because I want to take tomorrow off." or

"I need to finish this tonight, because I want to take tomorrow off."

or "I have to finish this tonight, my deadline is tomorrow."

In a softer tone, you could say:

"I need to finish this tonight, my deadline is tomorrow."

'Need to' is an ordinary verb

and takes auxiliaries.

"Do I need to finish this tonight?"

I don't need to finish this tonight."

You may also come across the modal verb 'need'.

It is not a very common modal verb and can only be used in negative

sentences and questions.

So you may hear instead of "do I need to finish this?"

"Need I finish this?"

or

Instead of "I don't need to finish this."

you may hear

"I needn't finish this."

Let's do a gap filling exercise now.

"Have you had your exam results?"

"Yes I've failed Biology.

I will ......

retake it in August.

I will have to retake it in August."

"Oh sorry.

You ......

be pretty upset.

You must be pretty upset.

What about Physics?"

"I've passed that but with a very low mark.

My teacher thinks I ......

retake that too.

My teacher thinks I should retake that too."

"Do you think you .....

retake it?

Do you think you should retake it?"

"No, I strongly feel that I ......

focus on biology.

I strongly feel that I must focus on Biology.

I ...... fail that one.

I mustn't fail that one.

I ...... get at least a B in Biology to study medicine at university.

I have to get at least a B in Biology to study Medicine at university."

"Did you fail Biology last year as well?"

"No I passed it last year.

I ......

have passed it this year too.

I should have passed it this year too.

I just didn't study enough."

"You ....... have studied enough! You always do."

You must have studied enough you always do.

The exam .....

have been difficult.

The exam must have been difficult."

No, the exam wasn't difficult. I was too tired.

I ......

have partied the night before.

I shouldn't have partied the night before.

I ...... have studied instead.

I should have studied instead."

Oh, I see. Well, you are good at Biology.

You ....... be able to pass it in August.

You should be able to pass it in August."

"I hope so.

I will ......

find a summer job as well. My dad insists!

I will

have to find a summer job as well."

"Did you have a summer job last year?"

"No, I didn't .....

work last summer.

I didn't have to work last summer.

I had some savings then."

"What happened to your savings?"

I ......

buy a car because my flat was too far from the college.

I had to buy a car."

"Well, good luck with your retake. You .......

let me know how it went.

You must let me know how it went."

Right, that's the end of this lesson, I hope you've enjoyed it.

As you know, you can now go to our website anglo-link.com for further explanations

and exercises.

Thank you for watching, I look forward to seeing you in our next video.

Bye now!