This article's title is a bit misleading. It's true that 'must' and 'have' are both modal verbs. However, to use 'have' as a 'helping' or 'auxiliary' verb, you must use it in its infinitive form: "I have to go to school", for instance.
Including 'to' in this construction signals that this 'have' works a modal verb in this sentence. Otherwise, 'have' works like any other transitive verb: "I have a new bike", as an example. Thus, the proper comparison for our topic is must vs. have to. Otherwise, you'll find no correlation between must or have.
How sneaky of us to introduce 'must vs. have to' that way! But don't dismiss all this information just yet; we had a reason for this small trick.
Language students are legendary for their leaps of intuition. English students of other languages (ESOL) master using the modal verb 'have to' quickly. And then, when introduced to 'must', many logically assume that 'must to' must be its proper form. Especially because many English teachers introduce this verb as a stronger form of 'have to'.
In fact, these two verbs are very different. Much like the modal verb pair will and would - and, indeed, most modal pairs, they represent contrasting meanings. So this article studies:
- the common roots of must vs have to
- the concepts 'have to' represent
- the secrets behind 'must's strong meaning
- examples of how to use each of these verbs properly
Among the common mistakes ESOL students make, "I must to go to home" and similar constructions rank high on the list. As an ESOL teacher, it was challenging to correct such mistakes, while still encouraging the intuitive leaps my students made. By the end of this article, you too will have to see that this particular leap is incorrect.
How Must vs. Have Became a Modal Pair
The verbs 'must' and 'have' came to modern English from the German tongue. German speakers will recognise them as versions of their verbs 'müssen' and 'haben'. However, they have different meanings in these languages, depending on how they're used.
'Must' is an old verb but it had a different spelling back then. The word 'moste' was the past tense of the root 'motan'. It meant 'to be obliged or forced'.
Before the 14th Century, Germanic and English speakers conjugated this verb. Over time, the 'motan' form fell out of use and the past tense form became the common form. By this time, its meaning had evolved to 'to have to' or 'to be able to'. Since then, it is only used in this form.
Two centuries later, 'moste's meaning transferred to 'have to', in the sense of 'possessing a duty'. Here, we get a clue of how this meaning broke away from the more forceful 'must'.
Now, let's examine these modals and understand how they should - or shall? - be used. We'll discover how 'must' became such a forceful command and why 'have' was linked to 'duty'.
Understanding the Strength of 'Must'
In the last segment, we learned that 'moste' was the past tense of 'motan', which meant 'to be obliged or forced'. We further studied how 'motan' vanished from dictionaries, leaving only 'moste', which became 'must'. Finally, we learned that, despite all those changes, this auxiliary verb kept its meaning.
This is where 'must' gets its strength. When you are forced to do something, that suggests that someone with more power is making you do it.
With that understanding, we can lay out 'must's qualities and properties. Its lack of conjugation might (or may) be the most obvious one; you can only use it in the present tense. Likewise, 'must' never gets an 'S' on the end, nor is it ever followed with a 'to'.
These are common mistakes ESOL students make when first studying this modal verb. However, it doesn't take long to master this verb's particulars.
Examples: "I must wait for exam results"; "You must do your work"; "They must clean the house"
Those examples all demonstrate an outside power dictating a person's actions. One cannot know their exam results until the examiner releases them. Therefore, they must wait. Likewise, when your boss tells you to get busy, your choices are to do so or get in trouble.
What about cleaning the house? That seems like a personal decision; something 'have to' might describe better. From just that sentence, we don't know if they were instructed to clean. Or maybe the house was so dirty, the speaker felt it was necessary to clean it.
Final note: many students wonder how to communicate past or future obligations if they cannot conjugate 'must'. In such cases, they must use the 'have to' construction. Unlike 'must', you may conjugate 'have to', as needed.
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Obligation and Necessity with 'Have'
The verb 'must' gives people an obligation; actions they must take out of necessity. Its partner modal, 'have' to, reflects acceptance of an obligation and necessity. To demonstrate this difference, compare these two sentences:
"I must go to the doctor" and "I have to go to the doctor".
The first sentence reflects a necessity; perhaps the person is sick. Illness is the 'outside force' that compels the action. By contrast, the second sentence reflects an obligation. Maybe the doctor called the person into their office to discuss a lab report.
These lines get a little blurry when talking about future and past obligations. Remember that 'must' does not conjugate. Therefore, future and past obligations demand 'have' in the required tense. "I had to go to the doctor" is yesterday's 'I must'. "I will have to go to the doctor" is its future version.
Before we move on, you might need some guidance about these modals' negative forms. For formal speech, you may simply insert 'not' after 'must': "You must not ever go in that room". However, it's more common to use 'mustn't': "You mustn't ever go in that room".
'Have' is a bit more complex. For the past tense, 'didn't' is the negative "I didn't have to go in that room". The future tense is: "I'll not have to go in that room".
What about 'Have got to'?
This is a slangy way to express an obligation. Native speakers use it to add emphasis; 'got to' doesn't change this modal phrase's function.
Typically, the conjugated 'have' is shortened to make the sentence flow better. As examples: "I've got to get my homework done!" or "He's got to help me!".
The only thing to watch for is adding a measure of time. "I've usually got to clean the kitchen" is incorrect. When time is a factor, you must use 'have to'.
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Clearing Confusion: Proper Usage of 'Must' or 'Have'
So when should you use 'must' and when is 'have to' correct? This question confuses even native English speakers. It's easy to understand why. Both of them communicate obligation, duty, responsibility, and necessity.
To see the differences between must vs have, it's best to compare them side-by-side. This table shows you when and how to use each one.
| Must | Have to |
|---|---|
| Personal choice or opinion | Based on fact, not opinion |
| Formal rules or instructions | Following rules or instructions |
| The speaker believes it's necessary | Someone else believes it's necessary |
| Only used in the present tense | Should be conjugated, if needed |
| Used in writing, especially formal writing | Used when speaking |
| Typically not used in questions | Commonly used in questions |
The rule to remember is as follows: If someone (or something) gives you an obligation, you must do it. If you receive an obligation, you have to do it. The following example shows the difference.
Your ESOL teacher says you must turn in your assignment tomorrow. You might tell your friends that you can't meet them later because you have to do your assignment. In other words, your teacher gave you an obligation. Your duty is to fulfil it.
Let's try another one: nurses must wear a uniform while on duty. This is a rule their employer has decided is necessary. The nurses might grumble: "We have to wear a uniform" because their boss made this rule, not them.
When speaking of other people's obligations, you must conjugate 'have'. We should say: "Every nurse that works there has to wear a uniform." Or "Nurses had to wear a uniform", and even "Nurses will have to wear a uniform".
One small note about using 'must' when asking a question. This construction is more common in British English: "Must you leave right away?". Younger generations are not as keen for this usage. However, as sarcasm, it's gaining ground: "Must you be such a fool?".
The more you learn about these two modal verbs and their usage, the easier it is to see that they're not at all alike. Mastering this modal pair may put you in the rare position of correcting native English speakers. Or, at least, you'll be able to spot their mistakes.
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