Should, Have to, Need to, and Must

For levels 2 and up

image by WTCC instructor ecparent

image by ecparent

What are the differences in these sentences?

  1. I should cook dinner.
  2. I have to cook dinner.
  3. I need to cook dinner.
  4. I must cook dinner.

Many students are confused about the words, “should,” “have to,” “need to,” and “must.” What’s the difference? Are they all the same? How do we use them? Let’s look at them one by one.


“Should” is a modal verb. Modal verbs do not change in form. We never add -s, -ing, or -ed to a modal verb. After a modal verb, we always use the base form of another verb (no “to,” no -s, no -ed, no -ing).

image by WTCC instructor ecparent

image by WTCC instructor ecparent

You can see here that we do not use “to” after “should.” You can also see that we do not change the form of “should” with different subjects. It stays the same with the subjects “I” and “he.” Finally, you can see that we use the base form of “cook” in these sentences. We do not use “to cook,” “cooks,” “cooking,” or “cooked.”

When we use “should,” we mean that something is a very good idea. It is not required, and it is not 100% necessary, but it is a very good idea. For example, when you go to the beach, you should wear sunscreen (special cream to prevent sunburn). Is it a law? No. You are not required to wear sunscreen. Is it 100% necessary? No. Maybe you are not going to stay outside for a long time. Maybe you have dark skin that doesn’t burn. Maybe you don’t care about the possibility of skin cancer in the future. Is it a very good idea to wear sunscreen? Yes.

Here are some more examples:

  • You should eat vegetables. – Vegetables are healthy. It is a very good idea to eat them, but it isn’t required, and you can live without them.
  • You should exercise. – Exercising is a very good idea, but it isn’t necessary or required.
  • You should not eat a lot of fried food. – When we use “not” after “should,” we are saying that something is a very bad idea. Eating fried food is a bad idea. You are allowed to do it, and it will not kill you immediately, but it is not a very good idea.


“Must” is also a modal verb. It does not change in form, and the verb after “must” is always in the base form. “Must” has two meanings. When the meaning is similar to “should,” it is a formal word. We use it often in rule books, assignments, and legal documents. We do not use it often in conversation with this meaning, but you might hear it in a formal speech. Look at these sentences:

  • Students must arrive on time and be prepared for class.
  • Job applicants must have good communication skills.
  • The tenants must pay rent on the 1st of each month.
  • In NC, drivers must turn on their headlights when they use their windshield wipers.

Here, “must” means that something is required. It is a rule, a law, or a requirement. The meaning is similar to “should,” but it is much stronger.

The other meaning of “must” is a little more difficult. We use it to make a logical conclusion. We don’t know something for sure, but we are making a very, very smart guess. For example, I can hear noises coming from my neighbor’s apartment. My neighbor must be home. I can’t see him, so I don’t know for sure, but I am guessing logically. Here are some more examples:

  • Yesterday, Marco was very tired, and he was coughing in class. Today, he is not here. He must be sick.
  • The dog is standing at the door. It is scratching the door and looking at me. The dog must want to go outside.
  • My phone turned off, and I can’t turn it on again. The battery must need to be charged.

If you are very uncertain, you can use “might” in all of these sentences, but if you are more sure, “must” is correct.

Have to

The meaning of “have to” is very similar to “must,” but “have to” is more common because it is less formal. We use “have to” very often in speaking and writing. When we use “have to,” we are saying that something is required or necessary. It is stronger than “should” and less formal than “must.”

“Have” is NOT a modal verb. The form changes depending on the subject (I have/You have/He has/She has). Also, we use have + to + base verb.

image by WTCC instructor ecparent

image by WTCC instructor ecparent

Notice that you always need “to” and the base form of the verb.

Need to

“Need” is also not a modal verb. The form changes with the subject (I need/We need/She needs/It needs), and we use need + to + base verb. When we use “need to,” we are saying that something is necessary.

  • You need to drink water every day.
  • Babies need to sleep more than adults.
  • Her tooth is broken. She needs to go to the dentist.

Which one is correct?

Sometimes it’s difficult to choose the correct word. Many times, they are all correct, but they have different meanings. These differences are usually small, though, so it’s not a big problem if you use the wrong one. Ask several Americans to complete these sentences. Do they all say the same thing? If not, what’s the difference?

  1. I (have to/need to) do my taxes soon.
  2. You (should/must) file your taxes by April 15.
  3. I (should/must) call my mother.
  4. She feels very sick. She (needs to/has to) call the doctor.
  5. We (must/have to) pay our rent on the 1st of the month.

Your Turn

Look and listen for examples of “should,” “have to,” “need to,” and “must” this week. Why did the writer or speaker use that word and not a different word? What does the person mean? Bring your examples to class, and talk about them with your teacher and classmates.

2 thoughts on “Should, Have to, Need to, and Must

  1. Hello thanks, for everything for all information you put in this blog, it is very helpful for me. My teacher explain us about the numbers, all my life I was curios about it and now I know. Thank you so much.

Leave a Reply

Your email address will not be published.