I must rewrite the follwing passage into passive:

They have to take new measures to prevent more flooding.

We use must when "it's our intention" and "have to" - when we can do nothing with the task or current situation and someone else is making the decision for us.

Since that, it would be better to say:

New measures must be taken to prevent more flooding.

instead of:

New measures have to be taken to prevent more flooding.

  • 2
    That distinction between must and have to doesn't always hold true. I must take this medication. I have to take this medication express the same idea. Both of your flood measures examples are OK. – Tᴚoɯɐuo Jan 4 '18 at 14:45
  • @Tᴚoɯɐuo, what are the conditions the choise depends on? – Anthony Voronkov Jan 5 '18 at 12:23
  • In my AmE dialect, you could use them interchangeably and never be wrong. You would simply sound a tad more formal than the situation might require if you used must, but only in certain circumstances. Again, in my AmE dialect, in conversation, have to is preferred for relatively minor tasks that need to get done, and must is preferred for more important obligations that need to be met. – Tᴚoɯɐuo Jan 5 '18 at 12:49

In most situations it seems that the two (must/have to) are interchangeable, but if splitting hairs there is a difference in consequences (in must cases the consequence being more dire). https://www.grammarbank.com/must-have-has-to.html

In your specific question, when I give my students passive voice exercises I generally expect them to use the same verbs. I would say that being that have to is used in the original sentence, it is probably best to continue it in your answer.


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