what is it?
Spanish uses the verb deber in two distinct constructions that carry different meanings. Deber + infinitivo expresses obligation — something that must be done. Deber de + infinitivo expresses probability or conjecture — a reasoned guess about what is likely true. A third related form, deberías + infinitivo (conditional), softens obligation into advice. Keeping these three uses apart is essential, because the presence or absence of de — and the choice of tense — changes the meaning of the sentence entirely.
when to use it
Obligation — deber + infinitivo: Use the present indicative of deber (without de) when you want to say that someone is required or expected to do something. The obligation can come from rules, duty, or necessity.
Probability or conjecture — deber de + infinitivo: Use deber de when you are making a logical deduction or an educated guess about a present or past situation. The speaker does not know for certain; they are inferring.
Softened advice — deberías + infinitivo: Use the conditional form deberías (second person singular) when you want to recommend something to someone without imposing. This is the standard way to give personal advice in Spanish.
In informal spoken Spanish, deber and deber de are sometimes mixed. In formal writing and in exams, the distinction above is expected and should be maintained.
formation
All three constructions follow the same basic pattern: a conjugated form of deber + (de) + infinitivo. The infinitive never changes. Only deber is conjugated.
| pronoun | obligation (deber + inf.) | probability (deber de + inf.) | advice (conditional + inf.) |
|---|---|---|---|
| yo | debo trabajar | debo de estar cansado | debería descansar |
| tú | debes estudiar | debes de tener razón | deberías estudiar más |
| él / ella / usted | debe llegar a tiempo | debe de ser tarde | debería hablar con él |
| nosotros/-as | debemos salir | debemos de estar cerca | deberíamos ir juntos |
| vosotros/-as | debéis escuchar | debéis de saber la respuesta | deberíais intentarlo |
| ellos / ellas / ustedes | deben terminar | deben de ser las cinco | deberían llamar |
The infinitive that follows can be any verb. The structure is always: [deber conjugado] + (de) + [infinitivo]. Nothing comes between deber and the infinitive except the optional de in the probability construction.
examples in context
common pitfalls
Adding de to an obligation: Writing «debes de terminar el informe» when you mean obligation is incorrect. The preposition de signals probability, not duty. For obligation, use deber + infinitivo without de: «debes terminar el informe».
Treating deber and deber de as interchangeable: These two forms are not synonyms. «Deben terminar» (they must finish — obligation) and «deben de terminar» (they must be finishing — conjecture) convey different meanings. Swapping them changes what the sentence says.
Using the present indicative for advice: Saying «debes hacer ejercicio» sounds like a strict obligation or even a command. When the intention is to give friendly advice, use the conditional: deberías hacer ejercicio. The conditional softens the tone and is the expected form for personal recommendations.
Three sentences, graded here. Nothing is saved and no account is needed.
Juan lleva semanas sin gastar nada; ___ estar ahorrando para algo importante. (poder)
Fill in the blank with the correct form of the verb in parentheses.