Let's take the following pairs of sentences:

  1. Ich weiß es, dass du zu Hause bist / Ich weiß, dass du zu Hause bist.

  2. Ich versuche es, dir zu helfen / Ich versuche, dir zu helfen.

  3. Es ist schwierig, das zu entscheiden, was man sagen kann / Es ist schwierig, zu entscheiden, was man sagen kann.

  4. Ich weiß, was du denkst / Ich weiß das, was du denkst.

Is there a rule to know when the das/es is necessary? And if/when it is, are "das" und "es" always interchangeable?

2 Answers 2


The simple answer is that das and es can be replaced by the subclauses you have in your examples. You don't need both.

So correct sentences would be:

Ich weiß was. - Was weißt du? - Ich weiß, dass du zu Hause bist.

Wer kann mir sagen, wer der Präsident ist? - Ich weiß es!

In the first sentence was = dass du zu Hause bist and in the second one es = wer der Präsident ist.

If you don't have a subclause, you have sentences like:

Ich versuche es. / Ich versuche das.

It doesn't differ so much in meaning as in tone or register. The usage with das might sound more blunt in some cases and a bit colloquial.

One exception might be:

Es ist schwierig, das zu entscheiden.

I wouldn't use es here, because there is also an es in the main clause which has a different function. das is something concrete, a specific question for example.


As sad as it may be, I don't think that there is general rule and it ultimately comes down to just pure usage. The "es" is wrong in all your example except 3. Not just optional but wrong. However, there are examples with the exact same structure where it is optional

Ich genieße es, dir zuzuhören.

Ich vermisse es, einen Strandspaziergang zu machen.

Here, the version with "es" is actually better. Without it it would sound truncated and in the second example, leaving it out can lead to grammatical confusion.

Ich vermisse einen Strandspaziergang... oh... zu machen.

As far "das" and "es"...no they are quite rarely interchangeable. If the "es" has only grammatical function (as in 3) or is optional (my example) then you cannot replace it with "das" because there isn't really anything "das" could point at. Only if the "es" is an full blown pronoun that refers to something that is not part of that very predicate, then you can replace it by "das" to get a stronger focus on it. But mind you, if you put emphasis, there has to be a reason to do so... for instance pointing out a contradiction.

Ich habe versucht, dir zuzuhören, aber es/das ist mir nicht gelungen.

In your third example, only "das" is possible, because it is a demonstrative pronoun that is "filled" with the relative clause. "Es" doesn't work like that.

  • Seems to me that the "das" in 3 is an object as well (the object of "zu entscheiden": what is being decided). We could say "Wir entscheiden das, was man sagen kann" to make it more evident.
    – persson
    Jan 9, 2014 at 0:02
  • @karoshi. ops, I though you were talking about the "es" in the beginning. You're right, the "das" is an object as well. But it is not purely grammatical, it is a regular demonstrative pronoun, which is filled afterward with a relative clause.
    – Emanuel
    Jan 9, 2014 at 8:30

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