‘must not’ in English and German

The English modal verb must and its German counterpart muss are cognates—they share the same origin and similar meanings. But when they are negated, they behave in different ways.

  • English Barbara must not go means that it is required that Barbara does not go.
  • On the other hand, German Barbara muss nicht gehen means that Barbara is not required to go.

To say that Barbara is not required to go, English uses a different modal verb: Barbara need not go. And to say that it is required that Barbara does not go, German also uses a different modal verb: Barbara darf nicht gehen.

One way to describe these facts is by using logicians’ and linguists’ concept of scope:

  • In Barbara is not required to go, the negator not takes scope over the modal form required to.
  • Conversely, in it is required that Barbara does not go, the modal required that takes scope over the negator not.

To show scope relations concisely and clearly, it is common to use the symbols ¬ for negation and □ for necessity. Using these symbols, the sequence □¬ means it is required that not. Conversely, the sequence ¬□ means it is not required that (and is permitted).

The following table summarises the use of English must and German muss when they are negated:

MeaningLogical
notation
EnglishGerman
required that.not□¬must notdarf nicht
not.required that¬□need notmuss nicht

Spelling German ‘muss

When I learnt German, the spelling of muss used the ‘scharfes S’ / ‘Eszett’ symbol as follows: muß. The ‘scharfes S’ / ‘Eszett’ (ß) was a compound letter consisting of an s (‘es’) followed by a z (‘zett’). A spelling reform begun in 1996 (and completed in 2006) replaced Eszett with a double s after short vowels, such as /u/ in the word muss.

For an example of Eszett in 19th century English, please see https://languagemiscellany.com/2021/11/an-old-way-of-writing-double-s/

You don’t need to write ‘need not

As I wrote at https://languagemiscellany.com/2021/08/you-need-not-understand/ the construction need not is becoming a little old fashioned. Non-native readers of English often find it hard to understand. So if I’m writing for non-native readers, I now use only an alternative version: does not need to.

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