Two Subjunctives

Question

What is the difference between the two from of the preterit subjunctive? When would you use them?

Answer 1

Short answer: you'll never go wrong with the -ra form.

Longer answer (and I'm sure there are a few threads on this already): When used as subjunctives, they are both equally valid, but the -ra form is used much more, especially in Latin America. The -ra form also has a few uses that the -se form lacks:

1) It can be an alternative to the pluscuamperfecto, as in "comiera" instead of "había comido".

2) It can used to soften requests or wants, or be a more modest way of stating things. The verbs used this way are "querer", "deber", "poder", "valer", and maybe a few others. Quisiera pedirte un favor, for example.

3) The same verbs (as in 2) can be used for the conditional, for example "Si la carretera estuviese buena, debieras llegar en dos horas".

Hope this helps!

Answer 2

Look at the link below. There are a number of posts but pay attention to Lazarus's answers on 20 August, one of which explains the two conjunctions.

Subjunctive

Also see Vikingo's explanantion above. - Eddy, Sep 13, 2009