What’s the difference between deber and deber de?
Introduction
The two verbal periphrasis deber + infinitive and deber de + infinitive have different meanings: deber + infinitive expresses an obligation and can be translated as must or be obliged to, while deber de + infinitive can only express probability or supposition, and can be translated as must be or must have.
Contents
Todos los conductores deben respetar el código de circulación y conducir con precaución.
El conductor de este vehículo debe de haber conducido muy deprisa.
deber + infinitivo
- The verbal periphrasis deber + infinitive expresses an obligation.
- It can be translated into English as must or be obliged to.
- Grammatically, the verb deber acts as a modal verb, it is conjugated to show the tense and mood in which the action occurs. The infinitive that follows expresses the action of the sentence.
- Examples:
- Todos las opiniones deben ser respetadas.All opinions must be respected.
- El alquiler debe pagarse el día uno de cada mes.The tenant must pay on the first of the month.
deber de + infinitivo
- The verbal periphrasis deber de + infinitive is used for deductions. It expresses probability, uncertainty and supposition.
- It can be translated into English as must be or must have.
- Example:
- Carlota aún no ha llegado. Debe de haberse quedado dormida.Carlota hasn’t arrived yet. She must have overslept.
deber or tener que + infinitive?
Similar to the English must for obligation, deber is also typically limited to formal and written contexts. The more typical way to express obligation in Spanish is tener que + infinitive, which is comparable to the English have to.
- Examples:
- Debemos salir ya, o llegaremos tarde.We must leave now or we will be late.
- Tenemos que salir ya, o llegaremos tarde.We have to leave now or we’ll be late.
However, deber and tener que are not always interchangeable. Sometimes deber is used as should; it expresses an obligation that is more subjective, gives advice or presents an opinion.
- Example:
- Debemos darnos prisa.We should hurry up.
In contrast, tener que expresses an obligation based on objective criteria.
- Example:
- Tengo que marcharme; tengo una cita.I have to go; I have an appointment.
For this reason, deber and tener que are not used indiscriminately in different tenses:
- Deber is mostly used in the present tense and in the conditional. It is rarely used in the future and preterite tenses or in the subjunctive mood.
- Examples:
- Debes hablar con propiedad.You must speak properly.
- No debes/deberías decir palabrotas.You mustn’t/shouldn’t say swear words.
- On the other hand, tener que can be used in any tense or mood.
- Examples:
- Todos los pasajeros tuvieron que presentar su pasaporte en la aduana. (preterite)All the passengers had to show their passport at customs.
- Todos los pasajeros tienen que presentar su pasaporte en la aduana. (present)All the passengers have to show their passport at customs.
- Todos los pasajeros tendrán que presentar su pasaporte en la aduana. (future)All the passengers will have to show their passport at customs.
- Es lógico que todos los pasajeros tuvieran que presentar su pasaporte en la aduana. (imperfect subjunctive)It’s logical that all the passengers have to show their passport at customs.