The use of vos instead of the more common tú as the second-person subjective pronoun.

In Argentina vos basically replaces tú in everyday speech among people of all classes and education levels.

It is very likely that vos developed in Argentina because it was probably the form that was used by the early Spanish settlers in that country. As Spanish overtook the indigenous languages of the country, people adopted the Spanish of those settlers. As this occurred in the days before electronic media, there would have been little outside influence that would have acted to make Argentine Spanish more consistent with that of other countries.

The conjugation for the "vos" in the present indicative differs from the standard second person singular (tú) in that the stress for the pronunciation lies on the last syllable, and not in the penultimate syllable: tú sabes -> vos sabés .

Although vos is universally heard in Argentina , it is used on a limited basis in southern Mexico , Central America, and northwestern South America . Its rules of usage vary with region, and it can be considered substandard usage in some areas. Some people use it with family members and very close friends.