A note on Voseo

So, most  some of you who study Spanish will know that Argentines use "vos" instead of "tú," the typical 2nd-person familiar pronoun. This phenomenon isn't unique to Argentina; it was used on occasion when I was in Costa Rica, and it was also used a little bit in Spain. It's also used in Colombia, Chile (weirdly), and Uruguay, among other places. In any case, Argentine is the only place I know of that consistently replaces "tú" with "vos" rather than use the latter as a linguistic spice and variation.

According to everything that I've read about "vos" and its variations, the standard, historical conjugation pattern was as follows: Take the "vosotros" (2nd-person familiar plural pronoun; its historical counterpart whose connection has long been broken), and remove the diphthong if there is one. Here are some examples:

In the present indicative:
tú sabes ... vos sabés ... vosotros sabéis
tú dices ... vos decís .... vosotros decís
tú comes ... vos comés ... vosotros coméis

In the preterite (simple past):
tú dormiste ... vos dormistes ... vosotros dormisteis
tú comiste ... vos comistes ... vosotros comisteis

In the present subjunctive:
tú comas ... vos comás ... vosotros comáis
tú digas ... vos digás ... vosotros digáis

In the present perfect:
tú has comido ... vos habés comido ... vosotros habéis comido

Now, it would be swell if everything worked out like I wanted it to, but Argentina is giving me quite an exercise in the "adaptability" and "patience" sectors of my brain. What's interesting from a descriptive point of view is that, although "vos" is used exclusively as a 2nd-person familiar pronoun here, the conjugation only follows my expected pattern in the present indicative. Of all 14 tenses and moods in Spanish, only one fits the pattern. Otherwise, the Argentine "vos" behaves oddly like two. It's just in the most common of tenses that we hear that sassy vos and get the resulting shift in emphasis.

Of course, it's possible that what I learned about voseo is totally wrong, too.

Food for thought: eat it up.