Our previous lesson explored the use of the verbs haber and deber to express obligation, requirement, or necessity. Let's now see how we can used them to express possibility or supposition instead.
We learned that the construction haber + de + infinitive is used to express obligation or necessity. The following example, however, shows that it's also possible to use it to express possibility:
Si mi vida ha de continuar... será por ti
If my life should continue... it will be for you
Captions 7-10, Belanova - Por tiPlay Caption
Of course, as you may have noticed, the use of the conditional si (if) plays an important role here. By using it, a sentence that would otherwise express a certain necessity, like mi vida ha de continuar (my life should continue), is transformed into one that expresses possibility. We can also use other words or phrases besides the conditional, for example, words typically used to express possibility, supposition, conjecture, or doubt. Here is an example using tal vez (maybe):
Tal vez ha de haber sido... un intento de mi parte.
Maybe it must have been... an attempt on my part.
Captions 24-25, Arturo Vega - Entrevista - Part 4Play Caption
However, sometimes we have to figure it out by the context. See for example this fragment of the song Marciano (Martian) by Mexican band Molotov:
No es el cuerpo marrano que solía tener, ni la cara, mi reina, que tú has de querer.
It's not the fat body I used to have, nor the face, my queen, that you probably want.
In fact, English is not unfamiliar with the use of "should" and "must" to express probability in sentences that rely on context for interpretation. Here are two examples:
Ha de tener hambre. | She must be hungry.
Has de querer que te de dinero. | You must want me to give you money.
You must also know that the expression ha de ser by itself means "perhaps" or "maybe":
Creo que ella es la ladrona. -Sí. Ha de ser.
I believe she is the thief. -Yes. Perhaps.
More interesting yet is the use of the verb deber (which is also a noun meaning "duty") to express possibility in Spanish. In our previous lesson you learned that deber + infinitive is used to express obligation. You also learned that it's grammatically incorrect, though common, to use deber + de + infinitive for the same purposes: you mustn't say debes de hacer la tarea, you must say debes hacer la tarea (you must do your homework). This is because deber + de + infinitive is reserved in Spanish to express possibility. Here are some examples:
Ah el... Este debe de ser el contrato.
Oh the... This must be the contract.
Caption 15, Muñeca Brava - 9 Engaños - Part 9Play Caption
So, in the case of the verb deber, Spanish uses two slightly different constructions: debe + de + infinitive for possibility, and debe + infinitive for obligation. Compare the previous example with the following:
Yo insisto en que éste debe ser el contrato.
I insist that this must be the contract.
Here is another example where debe de is correctly used to express possibility:
Así que creo que le debe de haber sido muy difícil.
So I believe that it must have been very hard for her.
Caption 47, Biografía - Natalia Oreiro - Part 6Play Caption
But, as we mentioned before, the use of debe + de + infinitive instead of debe + infinitive to express obligation is a very common mistake. We should avoid doing it, especially in written or formal Spanish. Not that it's a big deal, but below is one example (and you can find many more similar cases by searching our catalog):
Y esto lo debe de pagar* el cliente porque es de otro siniestro.
And this must be paid by the customer because it's from another accident.
Captions 17-18, 75 minutos - Gangas para ricos - Part 20Play Caption
*Y esto lo debe pagar el cliente is the correct expression.
The Mexican trio Belanova use the haber + de + infinitive construction repeatedly in the chorus of Por Ti:
Si mi vida ha de continuar
If my life should continue
Si otro día llegará
If another day will come
Si he de volver a comenzar
If I should start all over again
Será por ti
It will be for you
Captions 7-10, Belanova - Por tiPlay Caption
As it turns out, the haber+de+infinitive construction, often found in music and literature, is deceivingly difficult to translate with precision. A native speaker staff member tells us that, in the context of this song, she gets the sense that ha de continuar expresses possibility ("if my life is to continue / is going to continue") more than obligation ("if my life must continue"). However, generally speaking, haber+de+infinitive, does convey a sense of obligation or necessity, though often milder than the tener+que+infinitive construction (tiene que continuar -`"has to continue") or hay que+infinitive construction (hay que continuar -"has to / must continue").
For this reason, in the end, we chose to use "should" in our English translations as it is nicely ambigious, conveying a sense of possibility but also having the alternate meaning of mild obligation.
Note that haber+de+infinitive and hay [also from the verb haber] + que + infinitive are completely distinct, and used in distinct contexts. So, how should you decide de vs que? You see, hay que continuar, loosely translated as "one has to continue," would always express a generalization. Meanwhile, the first-, second- and third-person conjugations of haber -- that is, he, hemos, has, han, ha and han -- plus 'de' yields a more specific, though milder sense of obligation, or of possibility, as in our featured song.
A final note regarding the verbs in Belanova's provocative refrain: 'Volver a comenzar' could be translated bit by bit as "to return ['volver'] to begin ['comenzar']. But in English, we tend to say "to start again" or, with more emphasis, "to start all over again."