Spanish object pronoun

Spanish object pronouns are Spanish personal pronouns that take the function of an object in a sentence. They may be analyzed as clitics which cannot function independently, but take the conjugated form of the Spanish verb. Object pronouns are generally proclitic, i.e. they appear before the verb of which they are the object. Enclitic pronouns (i.e. pronouns attached to the end of the verb or similar word itself) may appear with positive imperatives, infinitives, and gerunds. In all compound infinitives that make use of the past participle, enclitics attach to the uninflected auxiliary verb and not the past participle(s) itself.

In Spanish, two (or rarely three) clitic pronouns can be used with a single verb, generally one accusative and one dative. They follow a specific order based primarily on person. When an accusative third-person non-reflexive pronoun (lo, la, los, or las) is used with a dative pronoun that is understood to also be third-person non-reflexive. Simple non-emphatic clitic doubling is most often found with dative clitics, although it is occasionally found with accusative clitics as well. In Castilian Spanish, and especially that of Spain's capital of Madrid, there exists the practice of leísmo; which is, using the indirect object pronoun le for the object pronoun where Standard Spanish would use lo (masculine) or la (feminine) for the object pronoun.

As the history of the Spanish language saw the shedding of Latin declensions, only the subject and prepositional object survived as independent personal pronouns in Spanish: the rest became clitics. These clitics may proclitic or enclitic, or doubled for emphasis. In modern Spanish, the placement of clitic pronouns is determined morphologically; by the form of the verb. They precede a conjugated verb but follow the infinitive or positive imperative form. For example: me vio but verme, viéndome, ¡véame! Exceptions exist for certain idiomatic expressions, like "once upon a time" (Érase una vez).

...
Wikipedia