1 The direct object is the element of the clause that under goes the action of the verb. The Spanish school students always listen that the way to distinguish a direct objectfrom other complements is toturn the clause into passive; but the foreign students do not always stand up the passive.
The verbs not admitting direct objectare called intransitive, although may take other complements. If they have direct object, are transitive.
The inside accusative is implicit in the meaning of some verbs: respirar (aire), vivir (la vida), dormir (un sueño), saltar (un salto), etc. This inside accusative does not turn the verbs into transitive; in fact they are considered intransitive.
2 Generally, the direct object is preceded by a in the next cases:
- With proper names of person.
Quiero a Julio José.
He visto a Silvia.
- With the personal, demonstrative, relative and indefinite pronouns referring to person.
Lo quiero a él.
No quiero a nadie.
- With nouns naming persons, if they are preceded by an articleor another individualizing element.
Quiero a mi familia.
Quiero al pueblo y ellos me quieren a mí.
- With the personified things (because of the habit of using a verb applied to persons).
Quiero a la justicia de mi parte.
- To avoid the ambiguities.
El cazador mató al tigre.
El tigre mató al cazador.
- With some verbs (sustituir, preceder, seguir) the preposition a is compulsary, even though referring to a thing.
El adjetivo sigue al nombre.
El nombre precede al adjetivo.
3 The preposition a is not used in the next cases:
- When the complement refers to things or places.
Veo un avión.
El ejército ocupó la región.
- To differentiate the direct object referring to a person from another complement, also referring to person, the preposition a is omitted before the direct object.
Prefiero el niño moreno al rubio.
To keep the preposition a before direct object referring to person, Spanish uses other expressions.
Prefiero a Marta antes que a Olga.
- In a clause with direct and indirect objects, both referring to person, may appear ambiguity. The ambiguity is solved placing the direct object next to the verb, and after it the indirect object followed by a.
He recomendado este chico al director. (= A boy has been recommended)
Presentaré la chica a mi amigo.
Si la situación se agrava hay que remitir el paciente a un especialista.
However, the preposition a is obligatory when the direct object is a proper name.
He recomendado a Luis al director.
- Another case is the verbs used with direct object referring to things.
Quiero un vaso de agua.
Robaron mucho dinero.
When the persons take the place of things, the preposition a is also omitted.
Quiero un taxista. (= I want to hire him.)
Robaron los niños del pueblo. (= They kidnapped children.)
The same clause with the preposition a has a different sense.
Quiero a un taxista. (= I’m in love with the taxi driver.)
Robaron a los niños del pueblo. (= Someone took something to the village children.)
- If a direct object referring to person is followed by another complement headed by the preposition a, the preposition that should precede the direct object is omitted.
Llevó los niños al colegio.