Have you ever wondered how que and de que are different, since both are frequently translated as "that"? Well, grammatically speaking, the distinction between que and de que is quite simple: que is used as a relative pronoun and de que as a conjunction. But that doesn't really solve the problem of learning how to use them for most of us, right? Let's see an example:
Una de las cosas que sé que tengo que hacer es ser...
One of the things that I know I have to do is to be...
Caption 65, 75 minutos - Gangas para ricosPlay Caption
How do you know that you can't use de que instead of que here? The answer is because que is being used as a pronoun, that is, to introduce a clause that provides more information about a noun, las cosas (the things). So by adding que the person talking is expanding the meaning of the noun cosas (things): it's not just the things, but the things (that) she has to do.
Now check out this example:
Tenía, como, el presentimiento de que me iba a pasar algo.
I had, like, the premonition that something was going to happen to me.
Caption 3, Club de las ideas - IntuiciónPlay Caption
The use of de que after a noun is that of a conjunction: it's simply used to connect words or groups of words, in this case a sentence with its subordinate. But how can you know this for sure? Here is a tip: try changing "that" to "which" in the English translation. If the sentence still makes sense, then you know "that" is being used as a relative pronoun and you should use que. Otherwise, use de que, as a conjunction. So, in the previous example you must use de que, because saying "the premonition which something..." just makes no sense in English. On the contrary, in the first example above, saying "one of the things which I know..." may not be common in American English, but it's still correct, and that's how you know that you must use the relative pronoun que. Keep in mind that this rule only works for sentences that use que or de que after a noun.
So, how do you say "I have the hope..." in Spanish? Do you say tengo la esperanza de que or tengo la esperanza que...? Cuban singer Alexis Valdes gives us the answer in his song "Canción de la semana" (Song of the Week):
Conservo la esperanza de que al final vendrás
I keep the hope that in the end, you will come
Caption 22, Alexis Valdés - Canción de la semanaPlay Caption
Now, you must know something. Don't get confused if you hear someone saying conservo la esperanza que al final vendrás or something similar. As in any other language, Spanish speakers commonly disregard grammar rules in everyday speech. In fact, using de que instead of que and vice versa are mistakes so common that they even have a name in Spanish: dequeísmo is using de que instead of que, while queísmo is using que instead of de que. By the way, these mistakes occur not only when de que and que are preceded by nouns, but also by verbs.
If you pay close attention, you will find many cases of dequeísmo and queísmo in our videos. For example, in the expression darse cuenta de que (to realize that) the preposition de (that) shouldn't be omitted but it usually does:
Tampoco sé si ella se dio cuenta que yo vi la bolsa de plástico.
I don't even know if she realized that I saw the plastic bag.
Caption 25, Dos Mundos - Escenas en ContextoPlay Caption
This is a classic case of queísmo. As you can see, the sentence doesn't pass our little test: you can't say "she realized which I saw the plastic bag," which means the word "that" is not used as a relative pronoun but as a conjunction. So to be grammatically correct you must necessarily use de que and not que in Spanish. And still, Spanish speakers say darse cuenta que, all the time! This teaches us language learners an additional lesson that is perhaps more valuable than all the grammar in the world, and that is: don't let grammar rules stop you from practicing your conversational skills. Native speakers speak real language (which linguists call el habla in Spanish), which isn't always grammatically correct.
Talking about overdoing things... Did you know that dequeísmo is usually the result of a hypercorrection in the attempt to avoid queísmo? Though dequeísmo usually only happens before verbs and not nouns. You can see this mistake in the following example:
Pero en la vida aprendí de que no se trata de "pobrecito"...
But in life I learned that it's not about "poor thing"...
Caption 2, Con ánimo de lucro - CortometrajePlay Caption
You must now be wondering: How can I know this is incorrect since our little "which-that" rule only works when de que / que comes after a noun? Simple: because you can never use de que after a transitive verb such as aprender (to learn). Never, ever. You must say: creo que entiendo (I think [that] I understand it), not creo de que entiendo; temo que dolerá (I'm afraid [that] it will hurt), not temo de que dolerá... etc.