Deber -vs- Deber de
Now that I have some street cred, I was wondering if my fellow language lovers could help me. I sort of asked in response to a previous post if anybody recognized a difference between deber and deber de. Might I have some insight from my fellow linguists.
"Deber" (conjugated) + infinitive = suggesting that something SHOULD, MUST, or OUGHT TO be done.
Debo limpiar mi carro. I should/must/ought to clean my car.
Debes lavar las vajillas. You should/must/ought to wash the dishes.
"Deber de" (conjugated) + infinitive = used to express a strong probability of something when you don't really want to suggest that something SHOULD happen, but rather something that MUST BE.
Debo de estar loco. I must be crazy.
Debes de ser la persona más alta que conozca*. You must be the tallest person I know.
So, our dictionary on the site isn't too explicit, but it is clear to see from deber that "deber de" means "it must be so" or a statement of a clear possibility as in "it could not be any other way, could it?"
If you feel your Spanish skills are up to the task you can take a look at this site.
Deber de + infinitivo expresa "possibility, assumption, conjecture or beliefs."
Deber + infinitivo significa "obligation," or a requirement, or sense of duty.
Take a look at the example sentences.
La diversidad que nos enriquece debe de unirnos en lugar de separarnos.
La diversidad que nos enriquece debe unirnos en lugar de separarnos.
The English equivalent of what we want the sentence to say is:
The diversity that enriches us should unite us rather than separate us.
Can you see which is better? " Deber de" or just " deber?"
We're not saying that being united naturally comes from diversity, but rather that if this were a perfect world that is the way that it ought to be.
The choice here is just "debe."
Let's take another example sentence.
Deben de ser las tres, porque la gente se va a comer.
Deben ser las tres, porque la gente se va a comer.
What we want to say here is:
It must be three O'clock, because the people are leaving to eat.
We choose debe de because it expresses an assumption or belief.
As a final example take the following two sentences:
Debería haber una ventana al otro lado.
Debe de haber una ventana al otro lado.
The first means "It really ought to have a window on the other side." (Like an architect might say if he were looking at your building considering the amount of sunlight your house gets.
The second means, not literally, "I believe there is a window on the other side."
However keep in mind the rules of language aren't hard and fast in the spoken world. Apparently this issue with deber and deber de is such an issue that natives must not always get it right since someone took the time to bother to write an article about it. Also, I'm not very good at understanding the formats of the RAE, but, from what it looks like "deber" can also be used to mean "deber de." Though if you can remember, try to use "deber de" in situations where it is appropriate rather than just always using deber.