Expressing Obligation and Probability using the verbs DEBER and HABER
 

Hi everyone. I do an Advanced Spanish Grammar podcast and my latest topic is using DEBER and HABER to express obligation and probability. Here are a few examples. I invite your comments and suggestions.

NOTE THIS IS AN EDITED VERSION OF MY ORIGINAL POST. I CUT OUT A BUNCH OF EXAMPLES TO MAKE IT EASIER TO READ.

Expressing OBLIGATION using the verb DEBER

¿Qué libro debo leer?
(What book should I read?)

Debes cepillarte los dientes dos veces al día.
(You should brush your teeth two times a day.)

To be more polite, you can use the conditional.

Deberías esperar a que él te llame.
(You should wait for him to call you.)

Here are two ways of expressing something that should have been done in the past using the verb DEBER.

Preterite/Imperfect of DEBER + INFINITIVE
Conditional of DEBER + HABER + PAST PARTICIPLE

Debimos decir la verdad.
Deberíamos haber dicho la verdad.
(We should have told the truth.)

Debías viver con nosotros.
Deberías haber vivido con nosotros.
(You should have lived with us.)

Expressing the obligation to pay for something using the verb DEBER.

Te debo una.
(I owe you one.)

No me debes nada.
(You don't owe me anything.)

Expressing PROBABILITY in the present using the verb DEBER + (DE)

Debo (de) estar enferma.
(I must be sick.)

Debemos (de) star soñando.
(We must be dreaming.)

Expressing probability in the past using the verb DEBER. + (DE)

Debimos (de) llegar tarde.
Debemos (de) haber llegado tarde.
(We must have arrived late.)

Debía (de) ser el más cualificado.
Debe (de) haber sido el más cualificado.
(She must have been the most qualified.)

HABER DE can be used to both express obligation and probability.
When HABER DE is used to express OBLIGATION it has a weaker connotation than TENER QUE.

He de estudiar esta noche.
(I should study tonight.)

Hemos de irnos pronto.
(We ought leave soon.)

HABER DE can also be used to express PROBABILITY, much like DEBER DE

Hemos de estar perdidos.
(We must be lost.)

Ha de haber un restaurante. por aquí.
(There must be a restaurant around here.)

HUBIERA + PARTICIPIO PASADO to express regret.

Me hubieras llamado. = Ojalá me hubieras llamado.
(You should have called me. = I wish you had called me.)

Hubieran venido a la fiesta. = Ojalá hubieran venido a la fiesta.
(They should have come to the party. = I wish they would have come to the party.)

Welcome to the forums!

I've given you some corrections above.

I just glanced over this one...

In Spain (at least) "¿Qué libro debo leer?" (Which book should I read?) is the most usual choice.

My mind was imagining a choice of a few books laying in front of me, so that's why I chose the interrogative I did. I would use 'qué' if I were thinking about 'what type of book' or if I weren't sure where to start.

Rusty! Thanks so much for the corrections. Me alegro de haber encontrado este foro. Y no volveré a poner enlaces en mis comentarios. :-) Y gracias también a JPablo por su sugerencia.

Am I right above, when I make the following phrases equivalent?

Debías vivir con nosotros. = Deberías haber vivido con nosotros.
You should have lived with us.

Debimos (de) llegar tarde. = Debemos (de) haber llegado tarde.
We must have arrived late.

I think I've also seen deber used like "tener que."

Debió salir temprano. = Tuvo que salir temprano. = He had to leave early.
Debí ceder mi asiento a mi hermano menor. = Tuve que ceder mi asiento a mi hermano menor. = I had to give up my seat to my younger brother.

Is that correct? If so, context is everything when trying to figure out the meaning.