Modal Verbs 2

In this section we will cover four modal verbs which can have shared meanings, but which also have different uses. They are:

• Must/ mustn’t – obligation, prohibition and strong advice
• Have to – Obligation and strong advice
• Should – advice
• Ought to – advice

The chart below outlines the basic form for each verb, its main uses and some sample sentences. This is followed by a more detailed explanation and exercises links. 

Before getting into the uses, rules and examples, it is important to note the following most common mistake:

• We DO NOT follow SHOULD and MUST with to, they are modal verbs and are followed by the base form of the verb. For example:

Must 

Must is a formal way to describe obligation, it describes things which are necessary. There are some important things to note about how we use must. 

1. It is very formal. We generally don’t use it in speaking. 

It would sound strange to say, ‘I must go now, I have to catch my bus’. Instead, we use ‘have to’ (see below). 

Must is used for formal rules, laws and procedures. We often see it on signs. 

2. We also use it for personal obligations. Things we think we should do. 

These are usually small things, which we might not have done for some time or which will have some negative impact. A similar phrase is ‘need to’. 

• I must check my bank account.  = I need to check my bank account. 
• I must try and eat less meat.  = I need to eat less meat. 

3. The negative form is a direct opposite, it cannot or should not happen. 

A similar phrase to ‘mustn’t’ is, ‘not allowed to’. For example:

• Students mustn’t leave the campus. 

Students are not allowed to leave the campus. 

4. Sometimes we use it to show strong advice. 

This is similar to should, but stronger, we also use have to in this way. This could be something small like a food or restaurant, something we have experienced and are recommending to friends, or something more serious, like medical advice. 

• You must try the new Italian restaurant on Main Street, it’s amazing!
• You must try to find time to relax, too much stress can be dangerous. 

Have to

Have to is similar to must because it describes obligation, something which is necessary. There are some similarities, but, more importantly, there some key differences. 

1. Have to is less formal, it is used in speaking instead of must. 

Whereas must is only used in formal situations, have to is used when speaking but can also be used in formal situations like business meetings. For example:

• We have to ensure that everything is in order. 
• Students have to wear a uniform at all times. 

2. Have to is NOT a MODAL VERB. So, he/ she/ it changes form and must use do/ does for questions and don’t/ doesn’t for negatives. 

So, the form is:

Using the 3^rd person correctly is the most common problem I have seen with ‘have to’, so getting the form correct is very important. 

3. Unlike MUST, the negative for HAVE TO, (don’t/ doesn’t have to) is not a direct opposite. 

Compare the following sentences:

1. You must wear a tie VS You mustn’t wear a tie
2. You have to wear a tie VS You don’t have to wear a tie. 

In sentences 1 and 2, must and have to mean the same, you are obliged to wear a tie, it is necessary. 

Whereas in sentences 2, ‘You don’t have to wear a tie’ means it’s not necessary, but you can if you like, it’s optional. 

So, we must be careful when saying that we ‘don’t have to’ do something, it means it’s optional, not prohibited. 

3. Similarly to must, we can use have to for strong advice or recommendations. 

Giving strong advice using ‘have to’ can be for something serious, for example:

• You have to quit smoking before it’s too late. 
• You have to tell him; he needs to know. 

However, it can also be for smaller, unimportant things like a movie, restaurant, book or TV show that we are recommending to someone:

• You have to read this book, it’s fantastic!
• Tis cocktail is delicious, you have to try it!

Should

Should is used for giving advice. It is a regular modal verb. It does not change form and it is used as for questions and negatives, for example:

• You should drive more slowly. 
• We should think about getting health insurance. 
• Should we try the new Italian restaurant? 

We also use should for things we expect to happen, based on routine or facts we are aware of. For example:

• John should be home in 10 minutes. 

However, this use of should is covered in the b2/ c1 section under ‘Modals 3 – deduction and speculation. 

Ought to

Ought to has the exact same meaning as should, but it is much more formal. It is not very commonly used because of its formality. For example:

• We ought to leave now or we will be late. 
• I think you ought to be very careful before you make a decision. 

In these examples the speaker would probably just say should, but ought to also works.

Although the negative and question forms do exist (as shown in the chart above), the question and negative forms are not used, it would be extremely rare to hear or see them used, even in formal speaking. 

Downloadable Exercises