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Must and have to are both used for obligation, according to Have to, must and should for obligation and advice.

However, I have come across to many sources with where they use must have to. On the contrary, my English teacher is highly against it as it sounds redundant in his opinion.

So, which one is correct?

  • It's hard to imagine what players must have to do to exercise their disciplinary committees. —The Guardian - Sport
  • You must have to pencil in a lot of people on your calender. —The Guardian - Business
  • A good pointer to the detail that engineers of smartphones must have to think about. —The Guardian - Tech
  • "What energy you must have to put yourself through something like that! —The New York Times
  • You must have to improvise, based on the actors in the show. —The New York Times
  • Just think of the courage a gay person must have to appear in televised discussions. —The New York Times

(screenshot)

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    It must be the case that you were/are/will be obliged to do something Aug 17, 2023 at 15:30
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    These aren't all examples of the same "must have to" and not all the "have to" examples mean "obliged to". Basically, they don't all mean the same thing. Some mean "[something] one is obligated to posses [in order] to [do something]". Also "you must have to" in 2 and 5 means something like "It would seem you are obliged to [do something]".
    – Billy Kerr
    Aug 17, 2023 at 15:46
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    Whenever you see must followed by have to, it's 100% certain that must expresses certainty (that something is indeed true). The have to part will refer to some obligation (the speaker is certain that the obligation exists). Aug 17, 2023 at 15:49
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    If you mean "It appears that you are obligated to fill in this form now", then yes. If you mean "You are obligated to fill in this form now", then no.
    – Billy Kerr
    Aug 17, 2023 at 15:54
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    @Ghost: Noe that your example #4 is a completely different construction. It doesn't involve coupling together the senses what must be the case + what someone is obliged to do - it's just the first of those senses attached to a statement about how much energy the addressee has. It must be the case that you have a lot of energy (nothing to do with obligation). Aug 17, 2023 at 16:46

5 Answers 5

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If you look at your examples, you can see that it is not redundant.

"Must" has many meanings. For example the Collins dictionary has 12 different definitions for "must" as a modal verb.

The 2 groups of meanings that are relevant are: "have to" as you have identified.

You must water the plants or they will die.

The other is "based on the available evidence, it appears that this is the case". For example, if Alice is in a room, and you go to that room and Alice is not there anymore:

Alice must have left.

Look at the second sentence in your screenshot:

You must have to pencil in a lot of people on your calendar.

This "must" is the second definition. It's expressing an opinion, something like

Based on what I believe your job is like, I think that you are required to [pencil in a lot of people on your calendar]


Some of your examples are not redundant because they don't actually contain the verb phrase "have to".

Just think of the courage a gay person must have to appear in televised discussions.

What energy you must have to put yourself through something like that!

In these examples, everything up to "have" is a clause expressing surprise or admiration, and the clause starting "to" is a qualifier or a reason that the person is surprised. You could actually insert a comma after "have", because "What energy you must have" is a valid statement on it's own.

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    Some of the examples might also be mistakes. It is hard to judge without context.
    – James K
    Aug 17, 2023 at 14:43
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    Yes, the first example sounds a bit off to me, I'd need to see it in context.
    – Ben Murphy
    Aug 17, 2023 at 14:44
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    @JamesK Hmm, seems borderline. "Would" would be clearer than "must".
    – Ben Murphy
    Aug 17, 2023 at 14:50
  • I initially found it hard to parse, but I believe the first example could be reworded as "need to have in order to do"
    – Barmar
    Aug 18, 2023 at 15:13
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The 'must' in these cases is not expressing compulsion, but an opinion of probability, certainty, or likelihood.

If you replace 'must' with 'likely', 'probably' or 'certainly', then you can see these examples are not tautological, even if they don't work quite as well as with 'must'.
That leaves 'have to' as the compulsion.

It's hard to imagine what players probably have to do…
You likely have to pencil in a lot of people…
the detail that engineers certainly have to think about

Try it the other way round, replacing 'have to' with 'compelled'. Again it's not always a comfortable structure, but the meaning is clear.

It's hard to imagine what players must be compelled to do…
You must be compelled to pencil in a lot of people…
the detail that engineers must be compelled to think about

As already noted, some of the examples aren't built from this structure. These could be clarified with a comma.

What energy you must have, to be able…

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    Yes, well explained. “Compelled” or in some cases “required” to. Example: “You must have to jiggle the doorknob to get the lock to work.” can be reworded to → “I guess you need to jiggle the doorknob to get the lock to work.” OR “It seems jiggling the doorknob is necessary to make the lock work.”
    – Mentalist
    Aug 18, 2023 at 0:35
  • I must've missed 60 Minutes. What are you saying?
    – Mazura
    Aug 19, 2023 at 20:10
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This usage of "must" with "have to" is very limited in scope and would not be used in general for the purposes you describe. I'm not an expert at grammar rules, but to me there are only a few specific sentence constructions and scenarios where it would make sense to use the two together this way.

Firstly, "must have to" could not be substituted for "must" or "have to" in general.

"I must have to go to the store"

does not mean the same thing as either

"I must go to the store"

"I have to go to the store".

The combined "must have to" is drawing a conclusion based on some premise. If you tell me that you are double majoring (working towards the requirements of two university degrees at the same time), I might comment that

"You must have to do a lot of studying."

I don't mean to instruct you to study a lot like

"You have to study a lot"

and I don't quite mean to state that you do study a lot like

"You must study a lot"

Instead I mean that as a result of your situation, you are probably obligated to study a lot.

So that is how I as a native speaker would interpret [must] [have to].

But a couple of your sentences are different:

What energy you must have to put yourself through something like that!

Just think of the courage a gay man must have to appear in a televised documentary.

In these case the phrase breaks down as [must have] [to]. For another example but without "to", "You must have a pretty impressive resume to have been selected for that job!" In this case, have is being used in the possessive sense and not the "have to" obligation or advice sense.

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If you are trying to express a thought like, “certainly need to,” or “necessarily was obligated to,” where either of two verbs with different meanings in the same clause could be replaced with must, you can replace either one with must (if the meaning is clear in context). For example:

You surely need to pencil in a lot of people on your calendar.

You must need to pencil in a lot of people on your calendar.

You surely must pencil in a lot of people on your calendar.

The version without must sounds overly formal to me, and I’m more likely to say either “must need to” or “must have to.” Also be aware that must cannot take a helper verb, so “*must must” and “*have must” are always wrong.

Your example uses have to instead of need to, but the same principle applies. Probably even more strongly: Neither “*had to have” nor “*have had to” sound idiomatic to me, so I’m especially likely to use an alternative such as “must have” or “have needed to.”

Several examples mean something else, however:

What energy you must have to put yourself through something like that.

Just think of the courage a gay man must have to appear in a televised documentary.

Both of these are examples of must as a modal verb modifying have, in the sense of necessarily possess, followed by an infinitive that begins with to. This appearance of have followed by to does not mean the same thing as have to. That example could have been phrased in several different ways:

What energy you must possess to put yourself through something like that.

What energy you must have in order to put yourself through something like that.

What energy you must have, to put yourself through something like that.

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There are different shades of meaning of "must". There's "obligated/forced", and there's "it's certain that". You can use the latter with "have to" to mean "it's certain that you're obligated".

Also, with the sentence "What energy you must have to put yourself through something like that!", "have" isn't a modal verb. "Have" isn't modifying "put". Rather, "have" is in this context a non-modal verb meaning "possessing" that goes with "energy": "What energy you must possess to put yourself through something like that!". The word "to" isn't a particle going with "have"; rather, it's a preposition heading the prepositional phrase "to put ...". The form "Must [verb]" can be followed by a variety of prepositional phrases, such as "You must buy this for the party".

Similarly, in "Just think of the courage a gay person must have to appear in televised discussions.", "have" is a nonmodal verb, with "courage" being the thing possessed.

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