Subjunctive

The example I have today is:

"Je suis triste que nous n'ayons pas pu venir"

and I'm wondering how or why "avoir" comes into it.  

The translation is: " I'm sad that we couldn't come" -

but the subjunctive for "pouvoir" is "nous puissions"

so can it be:  "Je suis triste que nous ne puissions pas venir"  ?

Help!


Emily

This one is more of a difference in context. The first case is a past subjunctive form (ayons pu), so it is a sentiment that refers to something that already happened (or the decision was already/previously made). For example, you were invited to a party, but you already made other plans, so you can't go.

With the second, "...que nous ne puissons pas venir", that would indicate that you are just making the decision now or just realizing now that you cannot go. For example, you planned on going to the party, but you can't find your car keys. (I'm sad that we can't come.")

Thank you - - so much to remember.....

Bonne explication. Je dois aussi faire attention au temps, car il est plus logique de l'explication et de l'intention de l'écrivain.