A specific question about IR
Hola.
Es mi pregunta aquí- Cuando ustedes "vayan" a Madrid, haremos una fiesta.
¿Por qué no usas "van"?
¡Gracias!
2 Answers
The subjunctive mood is used here because you are talking about a future event after "Cuando." Note that "Cuando" does not always require the subjunctive, but only when talking about an event that has not yet occured.
That's the subjunctive, and long story short, it's there because whoever is saying this sentence is not 100% sure when the people are going to Madrid. One of the main uses of the subjunctive is to show doubt or uncertainty, especially in cases like this where the action does not have a date but is something possible that could happen in the future.
Here are some links about the subjunctive: