“Must” and “have to” can be used to speak about obligations and probability. I’m going to divide this lesson into two parts.
PART 1 choices / obligations: You must wear a mask. / You have to wear a mask.
PART 2 probability / deductions: You must be Tim’s sister. / You have to be Tim’s sister.
You can watch my video lesson on this topic or keep scrolling to read more.
grammatical structures
subject + must + bare infinitive
I must go.
You must go.
He must go.
She must go.
It must go.
We must go.
They must go.
He musts go. She must goes. The form always stay the same with “must.”
subject + have/has to + bare infinitive
I have to go.
You have to go.
He has to go.
She has to go.
It has to go.
We have to go.
They have to go.
Remember to use “have” with he/she/it.
In informal English, you might see/hear:
I have got to go.
You have got to go.
He has got to go.
She has got to go.
It has got to go.
We have got to go.
They have got to go.
This form is correct and it means the same thing as “have to.”
PART 1: CHOICES / OBLIGATIONS
We use “must” and “have to” when we do not have a choice. We are speaking about obligations like laws and rules. These two verbs mean the same thing.
✔Citizens must pay tax.
✔Citizens have to pay tax.
✔Citizens have got to pay tax. (informal)
✔All students must wear a school uniform.
✔All students have to wear a school uniform.
✔All students have got to wear a school uniform. (informal)
✔If you want to hunt deer in these woods, you must have a hunting license.
✔If you want to hunt deer in these woods, you have to have a hunting license.
✔If you want to hunt deer in these woods, you have got to have a hunting license. (informal)
You can see with all of the above examples, you do not have a choice. If you don’t do these things, there will be consequences.
QUESTION: If these verbs can be used in the same way, are there no differences? Are they always exactly the same?
ANSWER: When it comes to rules and laws, “must” is more common in written English. It has a stronger and more formal feeling.
on a sign: Employees must wash hands before leaving the restroom.
Passengers must have a valid photo ID.
Children must be supervised at all times.
Applicants must submit their applications by the 15th of August.
In all three examples, “have to” is a correct alternative, but once again, “must” is mainly seen in written / formal contexts.
Be sure to check out my video for more examples.
When it comes to tenses, you need to change “have to” not “must.”
| RULES/LAWS
(no choice) |
past | present | future |
| MUST |
𐄂 Students |
✔
Students must wear a school uniform. |
𐄂 Students |
| HAVE TO | ✔
When I was in school, I had to wear a school uniform. |
✔
Students have to wear a school uniform. |
✔
Students will have to wear a school uniform next year. |
Yes, “must” can refer to the future, but the structure/ tense doesn’t change.
Students must bring a spare change of clothes with them on the trip tomorrow. will must
Things change in the negative. Let’s start by looking at the grammatical structures.
subject + must not + bare infinitive
I must not go.
You must not go.
He must not go.
She must not go.
It must not go.
We must not go.
They must not go.
subject + do / does not + have to + bare infinitive
I do not have to go.
You do not have to go.
He does not have to go.
She does not have to go.
It does not have to go.
We do not have to go.
They do not have to go.
In the negative, “must not” and “do not have to” become opposites. This is really important. Take a look.
must not = no choice
do not have to = your choice, there is no obligation
at a zoo: Visitors must not touch the animals. They do not have a choice. This is forbidden.
at a petting zoo: Visitors do not have to touch the animals. It is their choice.
during an exam: Students must not look at other students’ papers. They do not have a choice. This is forbidden.
during an exam: Students do not have to use a pen. They can use a pencil if they want. This is their choice.
Patients must not eat or drink anything six hours before the operation. This is forbidden.
Patients do not have to fast before the operation. They can eat and drink what they like.
Which sentence is unnatural?
1. You must not bring a gift to my birthday party.
2. You don’t have to bring a gift to my birthday party.
The first sentence is unnatural. The second sentence gives the guest a choice. “Must” is a strong word and it would be odd to forbid someone from bringing a gift.
personal obligations
What if we are not speaking about rules or laws? What if we are speaking about obligations coming from the speaker? Personal obligations.
“Must” is more common in British English and “have to” is more common in American English. However, many times it’s just personal preference.
More common in BrE:
I must stop worrying so much.
I must fix the sink today.
You must remember to thank Julie for the flowers.
More common in AmE:
I have to stop worrying so much.
I have to fix the sink today.
You have to remember to thank Julie for the flowers.
You can choose which verb you prefer.
We can remove the bare infinitive if the verb is obvious.
A: We should invite Dan and Julie to our party.
B: Do we have to? (Or less commonly: Must we?)
It’s clear in the conversation that person B means: Do we have to invite them? Must we invite them?
PART 2: PROBABILITY / DEDUCTIONS
We can use “must” and “have to” when we are 95% sure something is true/correct. We look at the evidence to form conclusions. This type of grammar is often called “probability” or “deductions.” You might see either term in your grammar books.
Nick always wears blue.
✔His favorite color must be blue.
✔His favorite color has to be blue.
✔His favorite color has got to be blue.
Do I know this 100%? Have I asked Nick what his favorite color is? No. I’m looking at the evidence to form a conclusion. Maybe Nick’s favorite color is red, but he just has a lot of blue clothes.
Leanne is a student in university.
✔She must be in her 20s.
✔She has to be in her 20s.
✔She has got to be in her 20s.
Do I know this? Have I seen Leanne’s date of birth? No. I’m looking at the evidence to form a conclusion. Maybe Leanne is only 18, but she looks 23 to me.
probability in the past and negative
present: Leanne must / has to be in her 20s. We are 95% sure.
present negative: Leanne can’t / cannot be in her 20s. We are 95% sure this is impossible.
You can see that we use “can’t / cannot” to express impossibility.
past: When Leanne graduated from medical school, she must have / had to have been in her 20s.
structure: must have + past participle (more common)
had to have + past participle (less common)
past negative: When Leanne graduated from medical school, she can’t have / couldn’t have been in her 20s.
Imagine you see this on a history test: What year did the Titanic sink? a) 1880 b) 1912 c) 1950
present: The answer must / has to be 1912. We are 95% sure.
present negative: The answer can’t / cannot be 1950. We are 95% sure this is impossible.
past: The Titanic must have / had to have sunk in 1912.
past negative: The Titanic can’t have / couldn’t have sunk in 1950.
“Had to have + past participle” can be a strange structure for many students. Firstly, it’s less common than “must have + past participle,” and secondly, “to have” is often contracted to “to’ve” in spoken English. It’s easy to miss.
So the diamond had to’ve gone down with the ship. (quote from Titanic 1997)
Maria had to have left you a note. She wouldn’t just leave without saying goodbye.
The witness had to have seen something else, but isn’t telling us.
In all of the above examples, “must have + past participle” is also a correct alternative.
TEST
Complete this test on the two parts from today’s lesson. Scroll down to the bottom of this blog for the answers.
| PART 1: OBLIGATION (choice) | PART 2: DEDUCTIONS (probability) |
1. Drivers _____ text while driving.
2. Christina _______ the project by Friday.
3. You ______ wear a costume to the Halloween party if you don’t want to. But, I think you should.
4. Last year, we _____ cancel our vacation because we all got sick. It was terrible.
5. Passports _____ be valid for at least six months if you want to travel internationally.
|
6. Burger Palace is always busy at lunchtime. Their burgers ____ be really good.
7. Ben goes to soccer practice five days a week. He ____ really love the sport.
8. Liam and Noah ____ be brothers. One of them is American and the other is Welsh.
9. I saw Sadie wearing the same sweater as me. She ____ bought it at the same place I did.
10. I ____ stolen your Amazon package. I was in New York on business last week.
|
Thank you so much for reading!
Don’t forget to check out my YouTube channel, Instagram, Facebook and other blogs. See you next time! Arnel
ANSWERS
1. Drivers _____ text while driving.
2. Christina _______ the project by Friday.
3. You ______ wear a costume to the Halloween party if you don’t want to. But, I think you should.
4. Last year, we _____ cancel our vacation because we all got sick. It was terrible.
5. Passports _____ be valid for at least six months if you want to travel internationally.
|
6. Burger Palace is always busy at lunchtime. Their burgers ____ be really good.
7. Ben goes to soccer practice five days a week. He ____ really love the sport.
8. Liam and Noah ____ be brothers. One of them is American and the other is Welsh.
9. I saw Sadie wearing the same sweater as me. She ____ bought it at the same place I did.
10. I ____ stolen your Amazon package. I was in New York on business last week.
|
