Test answers - Why the subjunctive?
I've just done the tests listed by Kiwi-girl here. In one of them I got three questions wrong because I used the indicative instead of the subjunctive. I've listed them below along with my translations. Can someone explain why the subjunctive is required in these cases?
Cuando vuelva de mi viaje, te llamaré - When I return from my trip I will call you
No he visto a nadie que lleve abrigo hoy, no hace frío - I have not seen anybody wearing a coat today, it is not cold
Tan pronto como sepa algo de él, te avisaré - As soon as I know something about him I will tell you
2 Answers
Read these two sections (seriously go the the main Spanish 2 Jehle page and read everything he wrote):
http://users.ipfw.edu/jehle/courses/subjadj.htm
The rule: In Spanish, the subjunctive is used in an adjectival clause when the antecedent is indefinite or unknown or is nonexistent or negated; in contrast, the indicative is used when the antecedent is a definite or existing one.
http://users.ipfw.edu/jehle/courses/SUBJADV.HTM
Adverbial conjunctions of time:
The following adverbial conjunctions deal with time, and are followed by the subjunctive when they introduce an anticipated situation.
(list includes cuando and tan pronto como).
Anticipated situations do not include habitual ones- cuando to mean every time (in the past and carrying through to the future even though it is not yet happened) is still in indicative.
Everytime I go to school- indicative
Tomorrow when I go to school- subjunctive
so:
Cuando vuelva de mi viaje, te llamaré - When I return from my trip I will call you--- anticipated situation
No he visto a nadie que lleve abrigo hoy, no hace frío - I have not seen anybody wearing a coat today, it is not cold - nonexistent person.
Tan pronto como sepa algo de él, te avisaré - As soon as I know something about him I will tell you- anticipated situation.
I can expound more if necessary.
The easiest way I find to think about it is .... are you wanting to declare the information as a fact (or something you believe to be a fact) - then use the indicative, if not, use the subjunctive. You might like to ask yourself questions like is it true? (indicative), or is it yet to come true (subjunctive, unless of course you are using the present indicative or future tense which allows you to declare the fact that you believe that something 'will' happen).
Sometimes when your sentence includes a number of pieces of information you may even need to ask yourself something like ... is this bit of information the focus of my sentence ie. Is the reason this piece of information is in the sentence is because I want to declare it (great use the indicative) or perhaps it's there to restate something already known, add a little background perhaps, set the scene with info that you and your hearer already know (then use the subjunctive).
Keep practicing and look out for examples given by native speakers and you'll soon get a feel for it 
