El Subjuntivo Presente
Expressing desire, doubt, and emotion
The subjunctive is a separate mood, not a tense. It appears in subordinate clauses after expressions of wish, doubt, emotion, necessity, and uncertainty. Most often introduced by 'que'.
Formation
For most verbs, take the yo form of the present indicative, drop the -o, and add 'opposite' endings: -ar verbs take -e endings, -er/-ir verbs take -a endings. 'hablo' → hable, hables, hable, hablemos, habléis, hablen.
Common triggers
Wish: 'Quiero que vengas.' Emotion: 'Me alegro de que estés aquí.' Doubt: 'Dudo que sea verdad.' Necessity: 'Es necesario que estudiemos.' Time clauses about the future: 'Cuando llegues, llámame.'
Two subjects
The subjunctive is only used when the main clause and the subordinate clause have different subjects. With the same subject, use the infinitive: 'Quiero ir' vs. 'Quiero que vayas'.
Ejemplos
"Espero que tengas un buen viaje."
I hope you have a good trip.
"No creo que llueva mañana."
I don't think it will rain tomorrow.
"Es importante que escuches con atención."
It's important that you listen carefully.