Temporal clause sequence and the subjunctive

These four rules determine which form of the subjunctive should be used in the dependent clause of a sentence consisting of main and dependent clauses:

1. When the action in the main clause precedes or occurs simultaneously with that in the dependent clause, and the main clause is in the present, present perfect, future, future perfect, or command tense, then the dependent clause will be in the present subjunctive form.
2. When the action in the main clause precedes or occurs simultaneously with that in the dependent clause, and the main clause is in the imperfect, pluperfect, or conditional tense, then the dependent clause will be in the imperfect subjunctive tense.
3. When the action in the dependent clause precedes the action in the main clause, and the main clause is in the present, present perfect, future, future perfect, or command tense, then the dependent clause will be in the imperfect subjunctive form.
4. When the action in the dependent clause precedes the action in the main clause, and the main clause is in the imperfect, pluperfect, or conditional tense, then the dependent clause will be in the pluperfect subjunctive tense.

In practice, the subjunctive isn't as complex as this mouthful would make it seem, but it is in fact difficult for the typical student of the language to internalize these rules. Entire books have been written on the subjunctive. True mastery outside of an immersion environment can take years. The keys are to study the subjunctive diligently, to pay close attention when you hear or see it used, and to imitate as best you can until you get it right. Pay special attention to it when you are reading. You'll probably find one or more of the rules to be easier than the others but you'll gradually improve at all four. Be persistent. Never give up!

Rule #1

Me alegro de que ustedes vengan.
I'm happy that you're coming.
Rationale: My happiness (present indicative tense) is occurring prior to your potential coming.

Les he pedido a ustedes que vengan porque necesito su ayuda.
I have asked you to come because I need your help.
Rationale: My asking (present perfect indicative) occurred prior to your potential coming.

Te pediré que vengas.
I will ask you to come.
Rationale: My asking (future indicative) will occur prior to your potential coming.

Rule #2

Me alegraba de que ustedes vinieran.
I was happy that you were coming.
Rationale: My happiness (imperfect tense) occurred prior to your potential coming.

Yo les había pedido a ustedes que vinieran porque necesitaba su ayuda.
I had asked you to come because I needed your help.
Rationale: My asking (pluperfect indicative) occurred prior to your potential coming.

Rule #3

Me alegro de que ustedes vinieran.
I'm happy that you came.
Rationale: My happiness (present indicative tense) occurs after your coming.

Me alegraré de que ustedes vinieran.
I will be happy that you came.
Rationale: My happiness (future indicative) will occur after your coming.

Rule #4

Me alegraba de que ustedes hubieran venido.
Me alegré de que ustedes hubieran venido.
I was happy that you had come.
Rationale: My happiness (imperfect or preterit tense) occurred after your coming.