Leísmo

Leísmo with animate objects is both common and prescriptively accepted in many dialects spoken in Spain, but uncommon in most others.

For example: Le and les are properly speaking the epicene indirect object pronouns, used for both masculine and feminine antecedents, whether animate or inanimate.

In certain dialects the reverse occurs and the indirect object pronouns are replaced by lo, la, los, or las (loísmo and laísmo), but this usage is not accepted by the Real Academia Española (Royal Spanish Academy): There are various diachronic and synchronic reasons for the use of le/les for direct objects.

There is a strong tendency in Spanish, inherited from Latin, for pronouns and determiners to have a set of three different endings for the three genders.

Thus, éste, ésta, esto; ése, ésa, eso; aquél, aquélla, aquello; el, la, lo; él, ella, ello.

This is known as leísmo de persona and is permitted by the Real Academia Española (RAE) only when used in the masculine singular (i.e. le to mean "him").

[1] The general tendency to use indirect objects for people also occurs when the speaker wishes to convey respect.

The general tendency to use indirect objects for people is intensified when the impersonal se is used instead of a real subject.

All of the theoretical reasons for using le/les detailed above actually influence the way Spanish speakers use these pronouns, and this has been demonstrated by various surveys and investigations.

García reports Buenos Aires natives differentiating between lo llevaron al hospital and le llevaron al hospital depending on how active the patient is, although anecdotal evidence suggests that Argentines are more loísta than this, and would prefer lo in both cases.