deber (de) + Infinitive

Obligation and Probability with Deber

Level 3

Deber + infinitive says what someone should do: Debes descansar (You should rest). It can also say what is probably true, usually with de: Debe de ser tarde (It must be late).

How It Works

Form. debo, debes, debe, debemos, debedes, deben + infinitive: Debemos saír cedo (We must leave early). Never put que or a between them; the only linking word deber can take is de (see below).

1. Obligation and advice. Deber says what is right, expected or advisable: Os pasaxeiros deben levar o cinto posto (Passengers must wear their seat belts). For a softer suggestion, use the conditional: Deberías durmir máis (You should sleep more). See polite requests with the conditional.

2. Probability. Deber also expresses a guess based on what you can see or know: Debe de estar canso (He must be tired), Deben de ser as tres (It must be about three o'clock). For a guess about the past, put deber in a past tense: Debeu de chegar onte (He must have arrived yesterday), Debía de ter vinte anos (She must have been about twenty).

With or without de? The Real Academia Galega dictionary lists deber + infinitive and deber de + infinitive as synonyms in both meanings, so Debes de ir falar con el (You should go and talk to him) is not an error in Galician. Keeping plain deber for obligation and deber de for probability is still a good habit, because it makes your meaning clear at once.

Negation. Non debes means "you must not": Non debes conducir tan rápido. That is different from Non tes que vir (You do not have to come), which only removes the obligation. See ter que.

Deber, ter que, hai que. Ter que stresses an obligation you cannot avoid (Teño que traballar). Deber is closer to what is right or advisable. Hai que and cómpre state a general need with no specific person.

Examples (6)

  1. Debes descansar un pouco.

    You should rest a little.

    Word by Word: Must-you rest a little.

  2. Os pasaxeiros deben levar o cinto posto.

    Passengers must wear their seat belts.

    Word by Word: The passengers must wear the belt put-on.

    A rule or obligation: plain deber.

  3. Deberías chamar a túa nai.

    You should call your mother.

    Word by Word: Should-you call the your mother.

    The conditional deberías softens the advice. The a here is the article, not a preposition.

  4. Debe de ser tarde, xa non pasa ninguén.

    It must be late; nobody is walking by anymore.

    Word by Word: Must of be late, already not passes nobody.

    A guess from the evidence: deber de.

  5. Debía de ter uns vinte anos cando marchou.

    She must have been about twenty when she left.

    Word by Word: Must-she of have some twenty years when left-she.

  6. Non debes conducir tan rápido.

    You must not drive so fast.

    Word by Word: Not must-you drive so fast.

    Non debes forbids; it does not mean "you do not have to".

Common Mistakes

  • Adding que after deber, as with ter que.

    Debes que estudar máis.
    Debes estudar máis.

    Que belongs to ter que and hai que. Deber is followed directly by the infinitive.

  • Adding a between deber and the infinitive.

    Debemos a saír ás oito.
    Debemos saír ás oito.

    Deber takes the bare infinitive; the only word it can take in between is de.

  • Using non debes to mean "you do not have to".

    Non debes vir á festa se non queres.
    Non tes que vir á festa se non queres.

    The intended meaning is "you do not have to come if you do not want to". Non debes means "you must not", which forbids coming. To remove an obligation, use non tes que.

How It Connects

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deber (de) + InfinitiveLevel 3Obligation and Probability with Deber

Learn This First

Deber with an infinitive expresses obligation, advice or probability according to context.

Words in This Pattern

deber