The Imperfect (Past) Subjunctive: When?

Remember that the subjunctive isn't a tense; it's a mood. That means that when to use it is determined by the situation, not by the time frame. So for the most part, all the reasons we learned to use the subjunctive in the present tense apply to the past as well.

Now before you have flashbacks to the nightmare of learning the difference between the imperfect and the preterite, a bit of good news; there is no "preterite subjunctive." Any time you need to use the subjunctive mood in the past tense, you will use the imperfect subjunctive (sometimes called the "past subjunctive").

So when do you need to use the subjunctive mood in the past tense? Read on.

(This page only deals with when you should use the imperfect subjunctive. To learn how to conjugate in the imperfect subjunctive, see The Imperfect Subjunctive: How?)

The Imperfect Subjunctive in Noun Clauses

All the rules regarding the use of the present subjunctive in noun clauses (namely volition, doubt, and emotion) apply to the imperfect subjunctive as well.

The following sentences in the present…

Mi padre quiere que yo corte el césped.
My father wants me to mow the lawn.

Yo dudo que ella sepa tocar el saxofón.
I doubt that she knows how to play the saxophone.

Ella está feliz que él vaya al baile.
She is happy that he is going to the dance.

Become these in the past:

Mi padre quiso que yo cortara el césped.
My father wanted me to mow the lawn.

Yo dudaba que ella supiera tocar el saxofón.
I doubted that she knew how to play the saxophone.

Ella estuvo feliz que él fuera al baile.
She was happy that he went to the dance.

The Imperfect Subjunctive in Adjective Clauses

In determining whether to use the subjunctive or the indicative in the present tense, we had to ask ourselves, "Is the antecedent definite or indefinite?" We'll ask the same question when dealing with the past tense. If the antecedent was concrete, we use the indicative (either preterite or imperfect). If it was non-specific, we use the imperfect subjunctive.

The following sentences in the present tense…

Tengo un libro que se trata de negocios.
I have a book that is about business.

Necesito un libro que me interese.
I need a book that interests me.

Become these in the past:

Tenía un libro que se trataba de negocios.
I had a book that was about business.

Necesitaba un libro que me interesara.
I needed a book that interested me.

The Imperfect Subjunctive in Adverbial (Adverb) Clauses

In the present tense whether or not to use the subjunctive in an adverbial clause comes down to the conjunction used. The same is true in the past.

Always Indicative

These conjunctions always require the indicative (in the present as well as the past) because they introduce facts: como, puesto que, ya que, dado que, en vista que, a pesar de que, por eso, porque.

This present tense sentence…

Rosa no va porque está enferma.
Rosa isn't going because she is sick.

Becomes this in the past:

Rosa no fue porque estaba enferma.
Rosa didn't go because she was sick.

Always Subjunctive

These conjunctions always introduce subjunctive clauses because the actions are uncertain or otherwise dependent on something else: antes de que, con tal que, en caso que, a menos que, para que, a fin de que, sin que.

This present tense sentence…

Nos dan clases de francés para que entendamos a la gente.
They give us French classes so that we understand the people.

Becomes this in the past:

Nos dieron clases de francés para que entendiéramos a la gente.
They gave us French classes so that we understood the people.

Subjunctive or Indicative

The following conjunctions could introduce either indicative or subjunctive clauses depending on the situation: aunque, cuando, después de que, hasta que, mientras que, siempre que, tan pronto como, en cuanto.

Use the indicative if the conjunction introduces a clause that refers to a habitual situation. Use the subjunctive if the clause refers to an action that had not yet happened.

These present tense sentences…

Usualmente me saludan tan pronto como llego.
Usually they greet me as soon as I arrive.

Voy a pagarte tan pronto como reciba el dinero.
I'm going to pay you as soon as I recieve the money.

Become these in the past:

Usualmente me saludaban tan pronto como llegaba.
Usually they greeted me as soon as I arrived.

Iba a pagarte tan pronto como recibiera el dinero.
I was going to pay you as soon as I recieved the money.

The Imperfect Subjunctive in Hypothetical Situations

If all of the information above hasn't convinced you of the need to learn the imperfect subjunctive, this might. We use the imperfect subjunctive when we talk about things that are hypothetical or contrary to fact. The imperfect subjunctive commonly appears in si clauses (si means "if") combined with an independent clause that contains a conditional verb.

By the way, this is a good example of one of the rare instances we use (or more accuarately, should use) the subjunctive in English. We often say things like, "If I was older…," "If I was president…," "If I was a millionaire…," etc. But we should actually be saying, "If I were older…," "If I were president…," etc. The subjunctive here indicates that we're using our imaginations and not talking about reality.

Some Spanish examples:

Si yo fuera maestro, nunca daría exámenes.
If I were a teacher, I would never give tests.

Nosotros entenderíamos si estudiáramos más.
We would understand if we studied more.

Si yo pudiera hablar portugués, viajaría a Brasil.
If I could speak Portugese, I would travel to Brazil.

Si tú estuvieras en mi posición, harías lo mismo que yo.
If you were in my position, you would do the same as I.

Yo compraría una casa si tuviera un millón de dólares.
I would buy a house if I had a million dollars.

As you can see, it doesn't matter whether the si clause starts the sentence or appears later. It is important, however, that the imperfect subjunctive verb appears together with the si. That's the hypothetical part. The conditional ("would") part of the sentence needs a conditional verb (obviously).

Other Uses of the Imperfect Subjunctive

Similar to above, we use the imperfect subjunctive in sentences with como si:

¡Habla como si fuera rey del mundo!
He talks as if he were king of the world!

We can use the imperfect subjunctive in sentences with ojalá or ojalá que:

¡Ojalá que entendiera matemáticas!
Oh, I wish I understood math!

And we can use the imperfect subjunctive as a substitute for the present tense or the conditional with verbs like poder, querer, and deber in order to soften the request or express courtesy.

¿Pudiera traerme un vaso de agua, por favor?
Could you bring me a glass of water, please?

¿Quisieras ir a la fiesta de Pablo conmigo?
Would you like to go to Pablo's party with me?