Understanding subjunctive I

I have always been taught that when using the subjunctive in the subordinate clause there must ALWAYS be a subject change from the main clause (with the exception of “if, then” and “as if/though” statements). However I’ve seen this “rule” broken in two books dealing with grammar and advanced conversation with no explanation as to why. For instance in one book I read:

-¿Qué harás cuando hayas terminado?

and

-Jugarán después que hayan trabajado


Thanks,
Ernestino

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Hi Ernestino,

There is no required subject change when it is a conjunction which introduce future or hypothetical action: "¿Qué harás cuando hayas terminado?" and "Jugarán después que hayan trabajado" are two good examples. Other examples: "Cuando termines, llámame." y "Lo haré en cuanto pueda".

- Karin