Nuances of meaning between "wo" and "weil/da"?

Question

Plaudern wir ein bisschen, wo du schon wach bist.

When the conjunction wo has the meaning of "as/since (you're already awake)", I wonder how it compares to using weil or da?

Answer 1

You will find wo used as subordinate conjunction very often in colloquial speech. But most teachers will not teach this usage of wo in schools.

Wo as a conjunction is considered to be not the best style. It is colloquial speech. You can hear it often when people are talking with friends, and you can read it in facebook and similar media that are dominated by colloquial speech, but chances are low to read it in newspapers and books.

Wo as a conjunction can be used in this ways (from Wiktionary):

• conditional

  Er half überall, wo möglich.

• modal

  Warum nicht jetzt sparen, wo man schon soviele Gelegenheiten versäumt hat?

• concessive, adversative

  Woher das schlechte Benehmen, wo Du doch am Hofe groß geworden bist?

Your sentence is an example for modal usage.

In all given examples you can replace wo by wenn, which is considered to be better style:

Er half überall, wenn möglich.
Warum nicht jetzt sparen, wenn man schon soviele Gelegenheiten versäumt hat?
Woher das schlechte Benehmen, wenn Du doch am Hofe groß geworden bist?

Plaudern wir ein bisschen, wenn du schon wach bist.

But you can't use weil/da in all cases without changing meaning. I show you by giving the English translations:

• Er half überall, wo/wenn möglich.
  He helped everywhere, if/when it was possible.

  Er half überall, weil/da möglich.
  He helped everywhere, becasue/since it was possible.

  The second is a valid sentence, but has a different meaning than the first.
  .

• Warum nicht jetzt sparen, wenn man schon soviele Gelegenheiten versäumt hat?
  Why not save now, if you have missed so many opportunities?

  Warum nicht jetzt sparen, weil man schon soviele Gelegenheiten versäumt hat?
  Why not save now, becasue you have missed so many opportunities?

  Usage of weil (becasue) does not make much sense here.

Answer 2

"Wo" would be used if the suggested activity is merely used to pass time or to put a (very) slight emphasis of unexpected, unrelated nature of the incident. Some, however, might even argue the difference is just a regional matter.

Another alternative to wo, weil or da is wenn, even though the phrase is a bit different: "Wenn du schon wach bist, können wir auch ein bisschen plaudern."