debe estar vs debe de estar

Question

I'm going over Pimsleur again using my notes and someone else's notes too. At one point they say "(Ella) debe estar contenta" and I have that written down, however, the other notes have Ella) debe DE estar contenta written, and when I look online there are many hits for "debe de estar". I am certain that Pimsleur is not saying de but,....What is the difference? Gracias.

Answer 1

I am not sure if there is a rule about this. I have heard both, and under this particular context, I understand both to mean the same thing.

I have found some general references that say that:

"Debe" mean an obligation and "Debe de", means a possibility.

So, perhaps we could think of this as " She must be happy" (debe estar), vs. "I bet she's happy" (Debe de).

I don't quite buy that in this context, but there you have it. To me both expressions mean the same, and the phrasing is just a matter of which form the speaker / writer learned.

There's an interesting thread about that subject here.

Answer 2

I just saw this question, I hope my answer will be useful in the future to other people. Very few people understand the difference, even few native Speakers do it, but the concept is very simple :

"Debe" means obligation and the literal translation is "Must". It comes from verb "Deber".

Example : El guardia debe estar en su puesto toda la noche / The guard must be at his post all night.

"Debe de" means probability and it is not related at all to the verb "Deber". That is the origin of the confusion. When you see "debe de" don't think about "debe", think about "Probably":

Example : El guardia no está en su puesto, debe de estar haciendo una ronda / The guard is not at his post, he is PROBABLY making a round.

The construction is : debe de + verb in infitive = probablemente + verb in present tense.

"Debe de estar" haciendo una ronda / "Probablemente está" haciendo una ronda / His is probably making a round.

You can also use it in past tense :

"Debió de ir" a hacer una ronda. / "Probablemente fue" a hacer una ronda / He probably went to make a round

You can't use it in future tense

nice post :) - Kiwi-Girl, Jun 28, 2013

Nice explanation! Also in the "probability" senario "must" is also used in English, hence the confusion for English speakers, ie: "He must be making his rounds / he is probably making his rounds". Saludos - 005faa61, Jun 28, 2013

I did not know that "must" can be possibility. Then what word is ? Should ? - kalki70, Jun 29, 2013