I was wondering how I can explain the subjuntif: My student created this sentance: "je suis triste qu'il n'aille pas à ma maison"
It isn't really the correct, but I think that the problem is that she used aller instead of venir. Is:
''je suis triste qu'il ne vienne pas à ma maison"
"je suis triste qu'il n'aille pas à Paris"
I think the choice between "aller" and "venir" has nothing to do with the subjunctive. It depends on where you are at the moment you speak.
if you are at your home, then he comes to your home - use "venir"
if you are not at your home, then he goes to your home - use "aller"
"to come" = "to go" towards the speaker, as viewed from the speaker's position