Here are two examples where de and que are meant to translate to to in English:

¿Dónde tengo que dejar los documentos? = Where do I have to leave the documents?

Es imposible de saber = It is impossible to know.

Both que and de mean to in these sentences. My question is what is the difference such that one must be used over the other?

2 Answers 2


Firstly, I need to say that's a really good question that Spanish learners ask often.

Well when you say in Spanish ¿Dónde tengo que dejar los documentos? you're actually asking a question: Where do I have to leave the documents?. It's an obligation.

Whereas, es imposible de saber it's an informative sentence, I mean, you're saying that It's impossible to know, without any reason.

So the main difference between Que and De is they are used depending the verbs and the context of the sentence. For example:

If say something that I have to do, let's say, my homeworks I'll say:

Tengo que hacer mis deberes (I have to do my homework)

But if I say something that's not an obligation; a normal sentence it will be, for example:

Las respuestas a mis deberes son imposibles de saber (It's impossible to know the answers to my homework)

As you can see, the que element is mostly used to say something you have to do and the de element is used for informative sentences. Hope it helped.

  • I tried to edit the answer to correct the sentence, as it's wrong, but it seems that the edit didn't go through the moderation queue. The correct sentence would be either: "Es imposible saber las respuestas de mis deberes" or Son imposibles de saber las respuestas de mis deberes (equivalent to: "Las respuestas de mis deberes son imposibles de saber, which sounds more normal"
    – pHonta
    Commented Mar 24, 2014 at 1:18
  • What about para in Tienes mucho para ofrecer?
    – David G
    Commented Mar 30, 2014 at 17:04

That's certainly a tricky question, and probably what's throwing you off is that "de" in your second example is attached to "imposible". It is used as a connector between the adjective (imposible, difícil, fácil, rápido) and the verb (in infinitive tense) that it's affecting.

However, in your first example, that "que" is a conjunction that links the main sentence (¿Dónde tengo XXXXX?) with the subordinate sentence (...que dejar los documentos).

Their purposes are completely different, and it's a coincidence (as far as I know) that the second "de" in english as to.

Don't try and draw a relation between them because they're translated the same. If I knew more about english, I could probably tell why "to" is used in both, but don't let that coincidence make you think there is any relation.

I hope I could clarify this up.

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