"I must do it" or "I have to do it"

Question

I would like to know the difference between "I must do it" and "I have to do it".

I am not sure the exact difference between "must" and "have to" in the other cases either.

Answer 1

Gramaticalmente, no hay ninguna diferencia entre I must do it y I have to do it. Son completamente intercambiable. Los dos quieren decir que es necesario que yo lo haga. Pero, por lo menos en el inglés del EEUU, hablar I have to do it es más común y más conversacional.

Pero, en la negativa, no son intercambiable.

I don't have to do it. (Hacerlo no es necesario)

I must not do it. (Hacerlo es prohibido)

Cuando digo "es prohibido," no quiero decir que la ley lo prohíbe. Es posible que yo me prohíbo por alguna razón como "I must not eat another cookie."

Muy bien dicho. Además, "Must" puede funcionar como algo que se supone. Por ejemplo, estás esperando gente quien no llege y piensas que la razón es mucho tráfico. "There must be a lot of traffic." - 005faa61, DIC 27, 2009

Answer 2

With don't have to is expressed lack of obligation or prohibition,

No. With "not have to" we can only express lack of obligation.

In short: very often must and have to are used in the same contexts. Sometimes, when we want to express an inner motivation, we use must:

I have to read this book. It's obligatory in the course I'm doing now.

I must read this book. I've heard it's really great!

I have to learn English. It's one of my compulsory school subjects.

I must learn English. I want to get a better job in the future.

Answer 3

I have to learn English. It's one of my compulsory school subjects.

I must learn English. I want to get a better job in the future.

I agree with Issa that these would probably be very common ways to express these ideas, but I just wanted to point out that the two (must and have to) would still be relatively interchangeable here:

• I must/have to learn English if I want to get a better job in the future.

• I must/have to learn English because it's one of my compulsory school subjects

• I must/have to read this book because it's obligatory in the course I'm doing now.

• I must/have to read this book. I've heard it's really great!

It makes the two phrases even more interchangeable when additional context is added such as this that clarifies whether the speaker is talking of a compulsion, obligation, necessity, etc.

htat's why I said that they're often used in the same contexts :)) I guess they used to be more distinct in the past - Issabela, DIC 27, 2009

Sorry...I wasn't trying to disagree with you. I was just trying to point out that with the addition of context, such as was provided, the two become very interchangeable. - Izanoni1, DIC 27, 2009

I agree with you; however, that in isolation, the phrase must often points to an inner obligation or need; whereas, Have to often points to something externally imposed. Again, I just wanted to stress the fact that this subtle difference becomes much... - Izanoni1, DIC 27, 2009

...less apparent with additional context - Izanoni1, DIC 27, 2009

No, I'm not saying that you disagreed :)) I just wanted to show, that we agree actually - Issabela, DIC 27, 2009

:)) - Izanoni1, DIC 27, 2009

Answer 4

Hi Nila

In most cases, I think the two are somewhat interchangeable as both can be used to indicate a necessity, obligation, requirement or compulsion. That being said, I think that when dealing with compulsion or doing something against ones will, the phrase "have to" is probably more often employed than "must."

• I have to (somebody is making me) eat the brussel sprouts.

• I must (should because they're good for me) eat the brussel sprouts.

Just keep in mind that these are my own personal observations as to how these to phrases are commonly used, but that according to their actual definitions, both should also be relatively interchangeable.

"Must" and "Have to" are identical in obligation. "Must" is simply more formal. "Should" is for giving advice - not obligation. - 005faa61, DIC 27, 2009

Good answer Izanoni. I would have to agree with you. Usually when one says "have to" it tends to be something someone is putting off or feels obligated to do. "Must" denotes the impression that one feels more motivated to do something. - Nicole-B, DIC 27, 2009

Answer 5

I hope I am not oversimplifying this, though. Must has other uses. For example, among other things, it can indicate a conclusion that logic seems to require.

Example:

He must have left already (he's not here and his car is gone, so, the logical choice is that he left).

Also, it gets muddled in past and future tenses because must has no past tense (one cannot say "musted") and no future tense (one cannot say "will must"). So, for positive expressions in past or future tense, anything that you would have used must for, you can express with "have to."

Example:

He must take the test / He had to take the test / He will have to take the test

In the negative, it gets more complicated. Using have to in the past or the future -- in the negative -- has the problem of indicating something is not necessary. It cannot indicate that something will be or was prohibited. So, when we try to express "must not" in the past we would usually say "should not have done."

Example:

You should not have stolen that car.

For the future, we can actually use the present tense by including phrases like in the future or going forward.

Example:

In the future, you must not copy Fred's homework.

Also, don't forget we can use other phrases besides must or have to. For instance, we can use words like require, prohibit, allow, etc.

Examples:

• He was required to take the test
• Back then, you were not allowed to stay out past 9 PM.

Is now a good time to point out that must is also a noun? - lorenzo9, DIC 28, 2009

:)) Brushing your teeth daily is a must. A cellphone with a full-qwerty keyboard is a must-have. - webdunce, DIC 28, 2009

Answer 6

Well, and what would happen if I changed the subject in the sentences?

You have to do it (tienes que hacerlo)

You must do it (debes hacerlo)

Here you cannot talk about an inner motivation or an inner obligation or a necessity....

Es lo mismo. "have to" y "must," en el positivo, quieren decir que hacerlo es necesario. Pero, en el negativo, "don't have to" quiere decir que hacerlo no es necesario, y "must not" quiere decir que hacerlo es prohibido. No importa cuál es el sujeto. Para los dos, la motivación o obligación puede ser interior o exterior.

Ejemplos en positivo:

• I must / have to go (because I promised myself I would)
• You must / have to go (because I told you to)
• They must / have to go (because the law requires them to)

Ejemplos en negativo:

• He doesn't have to go (he can go, but it is not required)
• He must not go (if he goes, he will suffer consequences)

Answer 7

• I have to (somebody is making me) eat the brussel sprouts.

• I must (should because they're good for me) eat the brussel sprouts.

Really? We the Spanish would say "tengo que comer ..." because from our point of view, it is a necessity. We use "tener que" for an obligation, and also for a necessity.

From our point of view........ - patch, DIC 28, 2009

Ah, yes. Then, under our point of view does not exist. Is that? - nila45, DIC 28, 2009

Answer 8

When I say "you must" do something, I generally mean "you ought to" do it, and NOT "you have to" do it. So I would use deber instead of tener que.

Answer 9

When the subject changes, in my opinion, the meaning can change slightly. Usually in English, when addressing someone and telling them of an obligation, we usually say "have to".

You have to clean your room tomorrow. You have to go to bed soon.

I think the term "must" is a bit old-fashioned. It is just not a word that is used often when giving a command. (At least in my opinion.)

However, the word "must" is generally used in friendly conversations, when someone is encouraging you to try or do something that they find enjoyable or profitable. For example:

You must try the seafood, it is excellent! or put in a more colloquial way: You have to go to an all-inclusive in Mexico. It is a must!

I am curious to see the ideas of others.

Answer 10

With have to is expressed obligation eg. In our school we have to wear uniforms. With don't have to is expressed lack of obligation or prohibition, like You musn't stay late.

The choise of the verb depends on whether the speaker expresses their own decision or reports the decision taken by someone else, eg. You musn't stay late. You've got a piano lesson. I can't stay late. I've got a music lesson. Must we use to talk about obligation to do ( or not to do - musn't ) something. Don't have to is the opposite of must.

Answer 11

Well, I have just found this:

"Must" and "have to" There are few differences between "must" and "have to" in these two sentences. Both of them express an obligation.

"Must" is used in present to express an obligation that comes from the person who talks.

I really must have my eyes tested.

You must be more careful, you know.

"Have to" is used to express an obligation that comes from outside.

You have to wear a safety belt.

You have to wear gloves. The instructions say so.

Answer 12

Well, and what would happen if I changed the subject in the sentences?

You have to do it (tienes que hacerlo)

You must do it (debes hacerlo)

Here you cannot talk about an inner motivation or an inner obligation or a necessity....

This is a great response. It works in the negative, too. You don't have to do it. (no tienes que hacerlo). - CalvoViejo, DIC 27, 2009

You must not do it. (No debes hacerlo) - CalvoViejo, DIC 27, 2009