"Deber" or "deber de"

Let's see!

Deber

There are two big meanings for this verb (without the "de"): obligation and to owe something/have a debt.

Obligation

Deber means to have an obligation

1. Debemos prestar atención en clase - We must pay attention in class.

2. Debes entregar los papeles a tiempo - You must deliver the papers on time.

The translation here is "must" because we're using present tense.
But see what happens when we change tenses:

1. Ella debía contarnos todo - She had to tell us everything.

2. Deberéis avisar si vais - you guys will have to tell if you go.

Past tenses or future tenses would be translated with had to/ has had to, will have to, is going to have to... basically, "to have to do something".

1. Deberías tomar un descanso - You should take a break.

With conditional we use "should" to translate it.

To owe

Deber also means to owe something

1. Me debes mil euros - you awe me a thousand euros.

2. Ellos te deben un favor - They owe them a favour.

Deber de

With de after, there's only one meaning: a supposition, an assumption, a guess.

1. Pareces cansada, debes de dormir mal - you seem tired, you must sleep badly.

2. Deben de haber perdido el partido, están muy decepcionados - they must have lost the match, they're very dissapointed.

3. Debe de ser difícil ver a tu ex con ella - It must be difficult to see your ex with her.

Practice

Choose between the following words to fill in the gaps below:
Debo, deben de, deberías, debe de, debíamos, deberás, debisteis.

1. Creo que _______ contactar a los padres antes. - I think you had to contact the parents earlier.

2. Queríamos coger el día libre pero _______ ayudar en la empresa familiar. - We wanted to take the day off but we had to help in the family business.

3. Después de la boda _______ estar cansados. - After the wedding they must be tired.

4. Sé que ________ tener paciencia. - I know I must have patience.

5. Ellos piensan que _________ ir a un especialista. - They think you will have to go to a specialist.

6. Mario ha conseguido un ascenso, _______ estar orgulloso. - Mario has gotten a promotion, he must be proud.

7. ___________ probar a meditar antes de descartarlo- You should try meditation before discarding it.

Sol: debisteis, debíamos, deben de, debo, deberás, debe de, deberías

Espero que haya sido útil! / hope it has been helpful!

¡Hasta la próxima! :)