El Imperfecto de Subjuntivo

In the paragraphe El uso del Presente de Subjuntivo you have learned when to use the subjunctive. In all the examples the main verb was in present tense and all the verbs in the subordinate clauses were in present subjunctive:
Quiero que venga Juan. (I want Juan to come.)
In this paragraphe you will learn when to use the past subjunctive instead of the present subjunctive. (For a complete description of when to use the present subjunctive, the past subjunctive, the present perfect subjunctive and the pluperfect subjunctive look under Sucesión de Tiempos .

In order to make this decision you have to answer two questions:

  1. What is the tense of the main verb (the verb in the main clause)? 
  2. When did the action of the subordinate clause occur in relation to the time frame of the main clause?
You have to use the past subjunctive or imperfecto de subjuntivo in the following cases:
  • when the verb in the main clause is in imperfect and preterite and the action of the subordinate clause happens at the same time or after the action or time frame of the main clause:
Ayer quería que Juan estuviera en clase. (Yesderday I wanted Juan to be in class.) (The "wanting" and the " being in class" happen in the same time frame = yesterday.)

Ayer dudaba que Juan estuviera en clase. (I doubted that Juan was in class.) (The "doubting" and the "being in class" happend both yesterday, in the same time frame.)

Quería que viniera Juan. (I wanted Juan to come.) (When I wished he would come, Juan had not arrived yet. The "coming" is after the "wanting".)

Dudaba que viniera Juan. (I doubted that Juan would come.) (When I doubted that he would come, Juan had not arrived yet. The "coming" is after the "doubting".)

  • when the verb in the main clause is in present tense and when the content of the subordinated clase is a description (with no specified beginning or end) in the past:
Dudo que el pescado que comí ayer estuviera malo. (I doubt that the fish I ate yesterday was bad.) (Subjunctive equivalent of: Sé que el pescado que comí ayer no estaba malo.)
  • in "if clauses" that refer to a situation contrary to the present truth:
Si tuviera dinero, iría al cine. (If I had money, I would go to the movies.) (I have no money [present truth]. If this was not true, I would go to the movies.)

In this kind of "if clause" you have to use the past subjunctive after "si" and the conditional in the main clause.

  • in wishes for the present and the past introduced by "Ojalá" :
Ojalá que viniera Juan. (I wish Juan could come.)

Ojalá que no estuviera nevando hoy. (I wish it were not snowing today.)