On “zu” and “um zu”

Hi there,


I’ve learnt about sentences with ‘dass’ and ‘zu + infinitive’, but I still don’t feel so confident writing arbitrary sentences that I make up myself. I’ve read the stuff on your site too and this helps loads (much more than many of the boring grammar books); but am still having trouble.

As I understand, it’s okay to write things like, “I know I eat many apples”, in two different ways:

Ich weiss, dass ich viele Äpfel esse.
Ich weiss, viele Äpfel zu essen.

But are they really the same? The literal English translation is slightly different:
I know that I eat many apples
I know to eat many apples

Also, I was wondering what is possible to make up the main bit of the sentence (“ich weiss”), not the dependent part. Can it just be anything that can be / needs completing? E.g.,

The sausages, …
On Tuesdays, …
I hope, …

For “I must have forgotten it”, would that be:
ich muß es zu vergessen haben.
ich muß haben, es zu vergessen.


(Originally asked by Edd)

6 comments on “On “zu” and “um zu”

  1. There are actually a few different question in this so let’s do them one at a time.

    There are indeed 2 ways to say “I know I eat many apples.”.

    – Ich weiß, dass ich viele Äpfel esse.
    – Ich weiß, ich esse viele Äpfel.

    But there is no version with zu. Why not? Well, first of there isn’t a “to” in English either and it wouldn’t make sense. The reason is that you can’t really “know” activities. You can know how to do them but knowing them is weird. English is a little more open with stuff like “I know swimming” but that would be “kennen” in German. Now, you can “wissen” a verb in German but that means something different.

    – Ich weiß viele Äpfel zu essen.


    I excel at eating many apples/I know well how to eat many apples.

    This is a very rare construction though.
    Ok… then what’s with this:

    – Ich weiß, ich esse viele Äpfel.

    This is common for very short introductory parts like “Ich denke, ich weiß, er sagte,…” You can then often skip the dass and connect the other information as a major sentence.. But in this particular example it only makes sense if you elaborate after that. It sounds “speech-y” so a speech has to follow :).

    Then… I don’t understand the second part of your question … the part with “the sausage, today, I hope”. I have a vague idea what you’re going for but it would be cool if you could explain a bit what exactly you want to know.

    And thus we get to number 3:

    – I must have forgotten it.

    This is not going to be a zu-construction either. Why not? well, firstly because there is no ” in English either. Any the reason is that “must” is a modal and modals connect the other verb directly, without zu/to that is.

    – I must forget it.
    – Ich muss es vergessen.

    – I must have forgotten it.
    – Ich muss es vergessen haben.

    I have done a quite in depth discussion of zu vs um zu on my blog. I don’t know if you’ve read it but in case you didn’t, here’s the link:


    And finally we get to the commas :)… the most simple advice in German is this:

    every action has its own sentence (major or minor) and those are separated using commas. Verbs in combinations with modals count as one action.
    There is a little uncertainty as far as REALLY short zu-constructs are concerned:

    – Ich versuche(,) zu schlafen.

    And the rule suggest we omit it (mainly because it looks stupid). But as soon as we add more information we’d have to use it.

    – Ich versuche seit Stunden, trotz des Lärms meiner Nachbarn ein bisschen zu schlafen.

    The comma tells us that a new verb is coming and that all the following information do NOT belong to the “versuche” directly. If the comma were missing there, I would trip if I read that out aloud.

    So… hope that helped a bit and let me know details about the second part :)

    • Edd says:

      Hi there,

      Thank you for your reply! Your answers always make sense, but in practise I must admit I’m still a bit confused (sorry!). I’ve also read your posts (even on zu, um/zu) and have found them really useful but evidently I keep making mistakes!

      My original question was intending to figure out whether a rule I had read (for when one can substitute dass with a zu+infinitive) always applies.

      Here were a couple of places online where I saw the rule (but I learnt it originally in a Goethe course I’m currently doing):


      Click to access BS2_inf_dass%20Info%20lg.pdf

      I thought that it was always okay to substitute dass with a zu+infinitive, if and only if the sub-clause had the same subject as the main clause.

      These websites give these sentences as example:

      Er glaubt, dass er es tun muss.
      Er glaubt, es tun zu müssen.
      He believes (that) he has to do it.

      Er meint, dass er es weiß.
      Er meint, es zu wissen.
      He thinks (that) he knows it.

      Es ist schade, dass man nur einmal jung ist.
      Es ist schade, nur einmal jung zu sein.
      It is a shame [that one is/to be] young only once.

      … and so I thought my own, slightly silly example would be okay :).

      Thanks for the nuances about wissen in your reply, and I see now my previous example was weird (didn’t sound right, and was wrong):
      Ich weiss, dass ich viele Äpfel esse.
      Ich weiss, viele Äpfel zu essen.

      Aside from my bad choice in verbs, was my application of the dass/zu+infinitive substitution wrong? As far as I can tell they have the same subject (ich)?

      Another example could be, e.g.,

      Ich denke, dass ich müde ist.
      Ich denke, müde zu sein.

      though I suspect the second sentence might be wrong too — but I just don’t know now :)!?
      (Thank you for teaching it’d be fine to say, “ich denke, ich bin muede”)

      Phew… I hope what I said made sense?!

      Regarding the second part of my original questions (“The sausages/On Tuesdays/I hope”), I was just anticipating that my failure to correctly substitute dass/zu+infinitive was because I didn’t fully understand what can constitute a valid main part of the sentence (before the comma). To be honest, I’m more than happy to just understand what I did wrong originally.

      Thanks again for reading all this and have a nice day!


      • Ah now I see where you got that idea… I actually have never thought about that and that’s why I didn’t say anything about it in the article on “um zu”.
        I would say this… forget it. A dass-sentence and a “zu”-sentence are not just 2 different phrasings that you can interchange at will. You will end up saying a lot of unidiomatic things… like:

        – Ich denke, müde zu sein.

        It is not wrong … it is just really weird.
        Same for this:

        – Es ist schade, nur einmal jung zu sein.

        I don’t know why they picked that as an example but I would never say that. The dass-version is definitely better.
        Ultimately it comes down to the verb, I guess. For some verbs the zu-construct is better, for others the dass-version. And for some, only one works.
        I have tried to find categories for the verbs but it is really hard. I think the zu-construct is less factual than the dass-sentence. So it’ll be better the more hypothetical your sentence is.

        – Ich sage, dass ich Hunger habe.
        – Ich sage, Hunger zu haben.

        Sagen is super factual. If you say something then you say it. Full stop. The dass-sentence tells us what you’re saying.

        – Ich behaupte, dass ich Hunger habe.
        – Ich behaupte Hunger zu haben.
        – I claim to be hungry.

        Claiming implies that it may not be so. Using the zu-construct here kind of underlines that. It sounds maybe 10% more like a false claim than the dass-sentence. Same for verbs like glauben or meinen… the zu-construct makes it sounds a little tiny bit less real at least to my ears.But then there are verbs like erlauben or verbieten. They sound better with zu and they don’t fit the system. So ultimately it is language in use I fear and you’ll have to pick it up over time. But you can’t just take a random sentence with dass and make it a zu sentence just because the subjects are the same.

        As for the second question…
        German and English are quite different when it comes to commas. In German commas do essentially 2 things… they order listings and they separate verbs. I main sentence will ALWAYS have to have a verb in it. German does not split of single pieces of information by a comma (unless they are an apposition)

        – Heute weiß ich, dass
        – Eine Wurst esse ich, weil..
        – Ich hoffe, dass…

        All those have in common that there is a verb in there.

        – Heute, …

        there is no verb in heute. So… a valid main part of the sentence has to have a verb. … hope that helps :)

  2. Edd says:

    Brilliant, that totally answers my question; loads clarified, loads of things for me to pay special attention to (when learning new verbs) — THANK YOU!!

    Have fun (also, great article on 2nd werden btw :))

  3. Anonymous says:

    Well as a German teacher in Turkey, I admired this blog. It is really helpful for people. In addition to reply by admin, I would like to also mention that even if the words can be used in a sentence without any grammar mistake, it still requires some other elements and one of them is semantics. In conclusion putting words together does not mean that you made up a sentence. I am not trying to offend you and sorry in advance if you are offended. Finally although languages are easy, please keep in mind that “Life is too short to learn German” by Richard Porson:)

    • Edd says:

      No offence taken, though perhaps we’re in agreement. I love learning German, and will continue — but, as part of the learning process I expect to make loooads of mistakes… and so I’m really glad this friendly forum exists to provide clear explanations of various aspects of the language, which really complement courses+grammar books. In fact, I usually find the explanations here make way more sense than grammar books and so on. I guess the stuff I’m alluding to here arises from the fact languages evolve (affected by loads of things like population migration/social factors, etc.), and aren’t 100% prescriptive. I’m pretty interested in all these aspects surrounding languages (like some of the things by Chomsky, etc.), though my favourite is still the plain old, trying to learn the language :).

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