Preparing for the 'oposiciones': The Subjunctive.

The subjunctive in English has only one form, which coincides with the base of the verb (the infinitive without to), and is the same for all persons without the addition of -s in the third person singular: She demands that you/he see her as soon as possible (ella exige que tú la veas/él la vea lo antes posible).
It could be said that the subjunctive has a limited use in contemporary English, but it can be found mainly in the following cases:

- in subordinate clauses introduced by that when the verb in the main clause expresses request, command, order, suggestion, etc., the so-called mandative subjunctive with verbs such as to demand, to order, to request, to insist, to suggest, etc:

They demanded that all political prisoners be released (Exigieron que todos los prisioneros políticos fueran liberados)
He insisted that the visitors be well treated (Insistió en que los visitantes fueran bien tratados)
My boss suggested that I take German lessons (Mi jefe me sugirió que tomara clases de alemán)

- in subordinate clauses introduced by that, when the verb in the main clause expresses a feeling or an emotion, the so-called emotive subjunctive:

It is strange that he refuse to see us (es extraño que se niegue a vernos)
I'm surprised that he behave like that (me sorprende que se comporte así)

- in subordinate clauses introduced by that, when the verb in the main clause expresses possibility, impossibility, supposition or necessity, the so-called putative subjunctive:

It is impossible that this go on much longer (es imposible que esto continue mucho más tiempo)
I prefer that he drive (prefiero que conduzca él)

In all three cases, there is an alternative with should in Br.E:

They demanded that all political prisoners should be released
I'm surprised that he should behave like that
I prefer that he should drive

Note

Were has a subjunctive value in some subordinate clauses and can be used, as well as was, to translate the Spanish past subjunctive:
If I were/was rich, I would buy you anything you wanted (si yo fuera rico, te compraría todo lo que quisieras); he speaks as though he were/was the boss here (habla como si fuera el jefe aquí); I wish the journey were/was over (ojalá hubiera terminado el viaje).
However, in the fixed phrases if I were you (si yo fuera tú) and as it were (por así decirlo), only were is used. 

Other constructions equivalent to the Spanish subjunctive

Apart from the subjunctive with should or the subjunctive proper, there are other constructions that can be used to translate the Spanish subjunctive, the most frequent ones being:

- Accusative + infinitive, with verbs that express command, request, permission, advice and wishing and their opposites (to want, to wish, to like, to love, to tell, to ask, to order/command, to beg, to expect, to allow, to advise, to forbid, etc.):

I want you to stay - quiero que te quedes
He told me to wait - me dijo que esperara
The doctor advised me to give up smoking - el médico me aconsejó que dejara de fumar

- I wish/if only + simple past, past perfect or would:

I wish I knew - ojalá lo supiera
I wish you had told me - ojalá me lo hubieras dicho
I wish she would marry me - ojalá se casara conmigo

- indicative mood: the indicative is frequently used in English, equivalent to a Spanish subjunctive, especially in the following cases:

a) adverbial subordinates of time:
I'll give him your message as soon as I see him - le daré tu mensaje tan pronto como lo vea

b) second and third conditionals:
If it rained, we would stay at home - si lloviera, nos quedaríamos en casa
If it had rained, we would have stayed at home - si hubiera llovido, nos habríamos quedado en casa

c) in various other subordinate clauses, where English uses the present, past, future or conditional depending upon the idea inherent in the clause:
I don't think he's in London - no creo que esté en Londres
I don't think she murdered her husband - no creo que ella asesinara a su marido
I don't think we'll go to Italy this year - no creo que vayamos a Italia este año
They're looking for someone who speaks Russian - están buscando a alguien que hable ruso
He disguised himself so that nobody would recognize him - se disfrazó para que nadie lo reconociera

For a complete treatment of other constructions used in English to translate the Spanish subjunctive see my Gramática Inglesa, 9ª ed., Pearson-Longman, chapter 12, pp. 330-339.

EXERCISE

Translate the following sentences into English, using the subjunctive proper or an appropriate alternative:

1.- Las órdenes del coronel son que ataquemos al amanecer.
2.- Si yo fuera tú, no me pondría ese vestido.
3.- Si yo supiera nadar, no me importaría ir contigo en esa barca.
4.- No creo que (él) lo haga.
5.- Llegamos a la estación antes de que saliera el tren.
6.- ¡Ojalá no me hubiera casado tan joven!
7.- El juez ordenó que el prisionero fuera liberado.
8.- Si yo fuera rico, iría de vacaciones a México.
9.- ¡Ojalá Carlos no fuera tan grosero!
10.- Insistimos en que sea llevado al hospital inmediatamente.
11.- Es urgente que tu padre venga a verme cuanto antes.
12.- Que yo sepa, el jefe no ha llegado aún.

KEY

1.- The colonel's orders are that we attack at dawn.
2.- If I were you, I wouldn't wear that dress.
3.- If I knew how to swim, I wouldn't mind going with you on that boat.
4.- I don't think he'll do it.
5.- We arrived at/got to the station before the train left.
6.- I wish I hadn't married so young!
7.- The judge ordered that the prisoner (should) be released.
8.- If I were/was rich, I would go to Mexico for my holidays.
9.- I wish Charles wouldn't be so rude.
10.- We insist that he (should) be taken to hospital immediately/right away.
11.- It's urgent that your father (should) come to see me as soon as possible.
12.- As far as I know, the boss hasn't arrived yet.