In addition to the example sentence, I have heard a lot of sentences similar to the title ones which uses those kinds of expressions.

I have gone through threads which explains "sein" vs "werden" in passive mode which explains some action has been completed or being completed. This confuses me.

Can anyone please help with an explanation with some more examples?

  • I am posting the question again here for clear visibility. Der Schalter muss in 5 Minuten geschlossen werden. (or) Der Schalter muss in 5 Minuten geschlossen sein. When I should use "sein" and "werden" to express the content.
    – Manushi
    Commented Oct 9, 2018 at 8:55
  • If my understanding is correct, first one is "the counter must become closed in 5minutes" and second one is "the counter must be closed in 5 minutes"
    – Manushi
    Commented Oct 9, 2018 at 9:01
  • The difference to the sentence in your question is that geschlossen is a perfect partiple (of schließen) so this sentence is passive. The one with werden is Vorgangspassiv (the most common form) whereas the one with sein is Zustandspassiv. They can both be translated as "The counter must be closed" but the former refers to the action of closing, the latter to the state of being closed.
    – RHa
    Commented Oct 11, 2018 at 14:57
  • Super. Now only I come across the term zustand passiv. It will help my learning further. Thanks.
    – Manushi
    Commented Oct 12, 2018 at 8:18

3 Answers 3


You can say both sentences, but they have different meaning.

"Sein" is "to be", and "werden" is "to become".

Du musst vorsichtig sein

refers to the present. Saying this I ask a person to change her or his behaviour immediately now. Or if the person thinks she or he is already cautiuos enough, she or he may answer: "Ich bin doch schon vorsichtig!" (I am being cautiuos already).

Du musst vorsichtig werden

refers to the future. Saying this I presuppose that the person I am speaking to is currently not cautious, and I admonish him or her to become more cautious at least in the future.

  • "Du musst vorsichtig sein" refers to the immediate future, not the present. At the present they are presumably not being careful enough
    – PiedPiper
    Commented Oct 8, 2018 at 8:55
  • @PiedPiper I think it depends on the concrete situation. When there is an immediate, present danger, it refers to the present. Imagine a child and a hot stove. You would not see the mother think "Little Joe has to be cautiuos in the future", rather she thinks "Little Joe has to be cautiuos right now." If the danger is seen as just forthcoming (and be it 1 second away) it refers to the future. Imagine somebody being warned about visiting dangerous places in a foreign country. - Problably there is no hard border between present and future in human mind. Commented Oct 8, 2018 at 15:56
  • Could anyone please give some example of the usage with sein and werden with the circumstance like the example I posted?
    – Manushi
    Commented Oct 9, 2018 at 8:50
  • I say a sentence "Er muss um 16 Uhr da sein.". Here "sein" is used not "werden". How I can differentiate where to use "sein" or "werden"
    – Manushi
    Commented Oct 9, 2018 at 8:52

"Du musst vorsichtig sein" is not passive as "vorsichtig" is not the perfect participle of any verb. It is simply an adjective.

Because of this, "Du muss vorsichtig werden" is not passive either. Which means that "werden" here is not an auxilliary verb but a full verb meaning "to become" or "to turn (into)". So the meaning is "You have to become careful", whereas "Du musst vorsichtig sein" means "You have to be careful".


More often than »Du musst vorsichtig sein« we say

Sei vorsichtig
(Be careful)

and »Du musst vorsichtig werden« is a very unusal way to speak. If at all, we say

Du musst vorsichtiger werden / sein
(You have to become / be more careful)

More common:

Du musst besser aufpassen
(You have to be more careful)

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