I think these two sentences have the same meaning, but which one should I use and why?

  • The sentence "Ich weiß nicht" is colloquial but IMO not complete since it's missing an object. It should read "Ich weiß es nicht". es or Das (in your case) referring to the question (its subject) that someone has been asked for. Commented Jun 21, 2014 at 19:44
  • 2
    I don't think it's missing an object. It's missing an indirect question which is left out as it is totally clear from the context.
    – bot47
    Commented Jun 23, 2014 at 7:38

4 Answers 4


The phrase

Ich weiß nicht.

is used in colloquial language to express uncertainty, doubt and disagreement, usually when asked for an opinion on something.

For example, I wouldn't be surprised to witness the following dialogue:

(Two girls in a shop)

A: Was hältst du von diesem Kleid?

B: Ich weiß nicht... - (thinks about it briefly) - Wenn du das nimmst, brauchst du jedenfalls auch passende Schuhe.

It is basically used as a filler in spoken language, much like a doubtful "Hm", to give the speaker a bit of time to think about how to phrase her doubts. Used like this, it is almost always followed by a pause and a more detailed explanation of the cause of the uncertainty.

The meaning depends a lot on context and tone of voice as well as facial expressions etc.

The phrase

Das weiß ich nicht.

means that the speaker actually does not know some fact.

A: Hat C seine Prüfung gestern bestanden?

B: Das weiß ich nicht, ich habe seither noch nicht mit ihm gesprochen.

As always when it comes to spoken language, the boundaries are a bit blurry and there are almost certainly regional differences.


In a context where one may say "I don't know" in English without any further elaboration, I think "Weiss ich nicht" would be more common than "Ich weiss nicht." However, other phases like "Keine Ahnung" may well be even more common in practice.

  • 1
    Hi and welcome to German Stack Exchange. While your answer’s details aren’t wrong, I think they just sli~ghtly miss the question. Not too bad in my opinion, but also not good enough to upvote. Do feel welcome and take a tour of the site!
    – Jan
    Commented Jun 12, 2015 at 16:50

1 Weiß nicht.

2 Weiß ich nicht.

3 Ich weiß nicht.

4 Ich weiß es nicht.

5 Das weiß ich nicht.

6 Das weiß ich wirklich nicht.

7 Das weiß ich leider nicht.

8 Keine Ahnung.

9 Ich habe keine Ahnung.

10 Ich habe keine Informationen.

11 Das ist mir nicht bekannt.

Jede dieser Formeln ist möglich. Ein kleines Kind könnte 1 benützen. Im lässigen Umgangston, unter Gleichgestellten, wird man 2-5 oder 8/9 hören. Wenn wir höflicher sein wollen, wird die Formel vollständiger sein. 10/11 ist mehr offizieller Ton.


Ich weiß nicht. = I don't know. (In a very general way. Could be in response to a specific question, where by context it is clear what specific thing you don't know, or could be generally expressing that you are at a loss regarding some topic, e.g. a philosophical question.)

Das weiß ich nicht. = I don't know that. (Refers to the specific piece of information someone sought. May imply that you don't know that, but do know something else.)

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