The subjunctive is a verbal mood that expresses doubt, desire, possibility, evaluation, emotion, indirect command, or purpose. It does not assert facts, but presents information as uncertain or dependent on another idea. In Spanish it normally appears in subordinate clauses introduced by que, para que, aunque, cuando, si, como, and others. The key is that it is usually required by the meaning of the main clause and not only by the verb. Mastery of the subjunctive involves recognizing when the idea depends on a result or is evaluative.

The present subjunctive is used for present or general situations that are not presented as facts, but as possibility, desire, intention, judgment, or necessity. It is formed from the first-person singular of the present indicative by changing the ending. For -ar verbs the endings are -e, -es, -e, -emos, -éis, -en; for -er and -ir verbs the endings are -a, -as, -a, -amos, -áis, -an. There are stem changes and frequent irregular forms, especially in the yo form and across the board for some verbs.

Some verbs have irregular forms in the present subjunctive because they change the stem or ending. Many coincide with the irregularity of the first person of the present indicative. There are also orthographic changes to preserve sound, such as c→qu or g→j before -a and -amos. Memorizing the most frequent ones makes it easier to recognize the subjunctive in real communication.

The imperfect subjunctive is used for unconfirmed past facts, for courtesy, or for hypothetical situations with si. There are two equivalent series in meaning: -ra and -se, though -ra is much more common in spoken language. It is formed from the third person plural of the simple past, removing -ron and adding -ra, -ras, -ra, -ramos, -rais, -ran. In subordinate clauses, it tends to appear when the main clause is in the past or conditional.

The present perfect subjunctive expresses anteriority with respect to the present in contexts of doubt, evaluation, or search. It is formed with haber in the present subjunctive plus the participle. It is typically used with expressions such as puede que, es posible que, dudo que, no creo que, antes de que and cuando in a non-factual sense. In many cases it equals 'it may be that already...' without asserting the result.

The subjunctive is used when the main clause expresses value, emotion, desire, indirect command, doubt, or unidentified search. It also appears with negation of belief or certainty, and with impersonal expressions that do not assert a fact. It does not depend solely on the verb, but on whether the information is presented as nonfactual or dependent. Often it is activated with "que" in a subordinate clause, but the decisive factor is the sense of the sentence.

There are typical combinations that select the subjunctive based on meaning, especially with "que". Desire and request typically appear with wanting that, asking that, needing that, or preferring that. Evaluation appears with is + adjective + that and with conviene that, importa that, es mejor that. Emotion appears with temer that, alegrarse de that, sorprenderse de that, molestar that. These structures function as triggers because they do not present the subordinate clause as a fact.

The indicative is used when the subordinate clause is presented as a fact, with belief, perception, certainty, or identified existence. In Spanish, the key opposition is factuality versus nonfactuality, more than formality. Expressions like creo que, es cierto que, está claro que, and el hecho de que tend to go with the indicative because they do not leave the content in suspense. Choosing between the indicative and the subjunctive changes the pragmatic meaning, not just the grammar.

In temporal clauses, the subjunctive appears when the action is future or hypothetical from the speaker's point of view. With cuando, hasta que, antes de que, en cuanto and mientras, the subjunctive is used if the action is not carried out. If the action is presented as habitual or already occurred, the indicative is normally used. The choice reflects whether there is anticipation and uncertainty, not just the temporal marker.

In the if conditional, the imperfect subjunctive is used for unreal or unlikely hypotheses in the present or future. The typical structure is if + imperfect subjunctive in the subordinate clause and simple conditional in the main clause. It can also be used with the imperfect subjunctive in both parts for greater distance or in formal registers. If + present indicative is used for possible or habitual conditions, not for contrafactual hypotheses.

There are differences in frequency and register in the use of the subjunctive, but the basic rules remain. In Spain it is common to use vosotros with subjunctive, while in America ustedes are used. The -se form (hablase) is more formal or literary, though it is correct in all dialects. In some areas the use of the indicative is favored among informal speakers in contexts of high certainty, but that does not change the standard rule.