Life into language: must vs have to

The most exciting parts of a language are probably those that reflect decisions the speaker must make in their real life. In the case of the present perfect versus the past, which was the subject of my last post, the speaker had to decide if the events they are talking about are still relevant as they speak, or if the events have turned into a “story”, or into history. 

In this post I’m writing about another real-life choice that the speaker must reflect on before selecting their words. I asked some students recently what they think the difference is between must and have to. For example, I must do it and I have to do it. Several guesses were made, but none was correct. 

I had to explain to my class that roughly speaking, both structures are the same, as they both mean that something is obligatory to do. But the problem arises especially when you want to use must / I have to, as well as You must / You have to.

In real life, obligation is a tricky matter. Where does the obligation come from? Whose rule is it? How much of the obligation is self-assumed, and how much is simply a no-choice situation? 

I must versus I have to force the speaker to decide if what they are under pressure to do is their own decision or not. I must apply for another job; this can’t go on like this – this is the speaker’s own decision to do something. I can’t do anything about it right now, so I just have to sit and wait – this is a no-choice situation; the speaker may not be happy with it, but they’ve got no alternative anyway.  The no-choice situation may be due to regulations, laws, procedures and rules, or due to the boss’s decision. 

You must versus You have to force the speaker to consider if they are putting pressure on their partner or they are just informing him / her about external restrictions. In other words, if you are trespassing my private property and I won’t have it, I will probably say You must leave this place at once. If we are sitting together in a cafe and you’d like to light a cigarette, I will probably tell you You have to put out the cigarette if you don’t want to get fined. In the first case, I’m saying it with my own authority; it’s my rule. In the second case, I’m saying it with no authority, as it’s someone else’s rule (the law). 

The dilemma about must / have to is not just a matter of deciding whose rule it is. It is also a matter of how abrupt you want to sound. Imagine yourself in the cafe telling your friend you must put the cigarette out at once!  It will sound very harsh and presumptuous. It will make it sound as if it’s you who have a problem with their smoking and as if you are forcing them to stop it. Or imagine that in the interview for your dream-job you say that you have to move on in your career; does that mean you are really enthusiastic about it?

Such examples of language choices show that a language is not simply a system of forms governed by some internal rules, for example subject comes first, after this verb use -ing, in this sentence you need this sequence of tenses etc. Language makes no sense without the real-life situation with the real-life partner. Whether you need to decide if you are self-motivated or not (I must, or I have to?), or whether you need to make it clear to your partner that it’s not you who’s forcing them to anything (you must, or you have to?), take care: you can’t make big language mistakes unless you’re making big reality mistakes.