When do we use have to and when do we use must? How about have got to? Or even gotta? Normally when we learn these two words, we are told that they mean the same thing - but is this really true? Let's investigate...
Must not vs Don't have to
It is true that must and have to mean similar things, however when we add a not the differences start to appear. Must not means that an action is prohibited, whereas don't have to means that something is not necessary. For example:
You must not eat in class.
You don't have to wear a uniform
Spoken and written English
This graph represents how common have to, must, have got to and gotta are in a collection of examples of British English. We can very clearly see that have to is much more common in spoken English and must is more common in written language.
Collocates are words which are commonly used together. If two words have the same meaning, you would expect them to be used alongside similar words. For must and have to this is true in most cases, but the few differences are interesting.
The following verbs appear with have to but not with must or have got to.
Farmers have to deal with all these challenges.
Well, we all have to face the reality that coherence starts at home.
Students and professionals who have to rely on their pens.
(Examples found on linguee.com)
These examples are all referring to general situations or obligations from external sources.
Have got to
The following verbs appear with have got to but not with must or have to.
Look grandpa, you've got to watch her!
He has got to pick up the goods and the costs for the empty container return.
We've got to pick up Diana as well.
(Examples found on linguee.com and the British National Corpus)
In these examples, we can see that there is either a direct order or a more specific obligation than in the examples for have to.
In short, these words have very similar meanings, however there are some general differences to remember to use them more naturally:
Is much more commonly used in written language
Is more formal
Is the most commonly used option
More frequent in spoken English
Can refer to obligation caused by external sources or situations
have got to
The have is almost always contracted (I've got to, She's got to etc)
Almost never found in written English
Refers to a direct order or a specific duty