deber or tener que?

Question

Which is the best one for "to have to do something"'

Answer 1

Both mean pretty much the same, but:

"Tener que" is something necessary in absolute terms.
"Deber" is something necessary according to the speaker's own judgement.

In practice both are often used interchangeably by many natives.

By the way, "deber" is followed by an infinitive, not "que". E.g. Debes estudiar.

Answer 2

I have heard some native speakers say something to the effect of "Debes de estar estudiando" Is there much of a difference between that and "Debes estudiar"? Or is the example I offered grammatically incorrect?

They are different. Debes estudiar means "you ought to study," while Debes de estar estudiando means "You must be studying," that is, I presume you are studying. Deber de + verb means that the speaker believes the truth of the verb.

Answer 3

The big difference is in the negative form - "no debes" is an obligation not to do something, while "no tienes que" is the absence of an obligation. Quite similar to English.

Answer 4

They are different. Debes estudiar means "you ought to study," while Debes de estar estudiando means "You must be studying," that is, I presume you are studying. Deber de + verb means that the speaker believes the truth of the verb.

hji James and endless, this is true, however we often use them inorrectly in Spanish. we might not even be able to say "incorrectly" here, as many well known writers use "deber de" in the sense of "deber".

You can read about this (mis)use here:

a) deber + infinitivo. Denota obligación: «Debo cumplir con mi misión» (Mendoza Satanás [Col. 2002]). Con este sentido, la norma culta rechaza hoy el uso de la preposición de ante el infinitivo: «Debería de haber más sitios donde aparcar sin tener que pagar por ello» (Mundo [Esp.] 3.4.94).

b) deber de + infinitivo. Denota probabilidad o suposición: «No se oye nada de ruido en la casa. Los viejos deben de haber salido» (Mañas Kronen [Esp. 1994]). No obstante, con este sentido, la lengua culta admite también el uso sin preposición: «Marianita, su hija, debe tener unos veinte años» (VLlosa Fiesta [Perú 2000]).

Answer 5

Both mean pretty much the same, but:

"Tener que" is something necessary in absolute terms.

"Deber" is something necessary according to the speaker's own judgement.

In practice both are often used interchangeably by many natives.

By the way, "deber" is followed by an infinitive, not "que". E.g. Debes estudiar.

So Lazarus, I have a question stemming off from your comment. I have heard some native speakers say something to the effect of "Debes de estar estudiando" Is there much of a difference between that and "Debes estudiar"? Or is the example I offered grammatically incorrect'

Answer 6

Oh ok. thanks!

Answer 7

I believe tener que is normally used when must do is implied and *debe que *is used when ***ought **to do* is implied. Of course, it all hinges on context.