2.6.3 Must

Examples of errors:

1. The art school is too far away. It must be easier to reach.
2. For an unwed mother, I think a legal abortion must be possible.
3. When a couple is sure from the beginning on that they don't want a baby it must be legal to abort the fetus.
4. It should be larger or there must be another one like it.
5. But she must have the decision, not some unknown doctor.
6. When the husband earns a lot of money the wife must not work.
7. I must not pay for my cigarettes. That's why I smoke.
8. The author means you must not be intellectual to learn a foreign language.
9. Young p eople are glad that they themselves must not cope with the problems of retirement.

Must is used in senses parallel to should (in sense 2--cf. above), but more emphatically-.or categorically; i.e. where should or ought to indicates desirability and moderate probability, must expresses necessity or obligation and high probability. (l)-(5)-describe situations that do not exist but are desirable, so should (sense 2) or ought to is the most appropriate form. It is true that the desirability of a state of affairs can sometimes be expressed emphatically or rhetorically by expressing it as a necessity or obligation, in which must is conceivable (e.g. Unemployment must be eliminated!). This rhetorical tone is not appropriate in the contexts in which (l)-(5) occur, however. Furthermore, as Leech (1971:§115) points out, must in this sense normally requires that the speaker is the person in authority, the one who is imposing the obligation. For example, a sentence like Unemployment must be eliminated! would be assumed to have been uttered by a politician, or member of a political party, who would conceivably be (or hope to be) in a position to exert some influence on the situation. This implication of the speaker's authority is not appropriate in (l)-(5).

A particularly important restriction on must for German speakers is that must not is not equivalent to müUssen nicht. Müssen nicht expresses the lack of obligation; must not expresses negative obligation--the obligation not to do something:

lack of obligation

Du mußt nicht hingehen.
You don't have to go.
You needn't go

negative obligation

Du darfst nicht hingehen.
You musn't go.
You can't go.

In (6)-(9) lack of obligation is the intended meaning, for which don't have to or needn't/don't need to is the correct expression.