In any language (Spanish or otherwise), the subjunctive isn’t a tense, which tells when an action took place: present, past, or future. Rather, the subjunctive is a mood, meaning it indicates how the speaker feels about or perceives a situation rather than when an action occurred. The subjunctive mood exists in several tenses: the present, the preterit, the imperfect, and the pluperfect.
It also makes even the hardiest of Spanish students quiver in their boots. But it doesn’t have to. The subjunctive really isn’t as difficult as it appears; if you can form the present tense, you can form the present subjunctive with any type of verb, because many of the subjunctive stems use the yo form of the present tense. With some practice, you’ll quickly become comfortable using it.
How is the present tense different from the present subjunctive? The present tense functions in the indicative mood — a mood that states a fact. The subjunctive (in any of its tenses), on the other hand, expresses unreal, hypothetical, theoretical, imaginary, uncorroborated, or unconfirmed conditions or situations. These expressions are the result of the speaker’s doubts, emotions, wishes, wants, needs, desires, feelings, speculations, or suppositions. Here’s an example of the difference:
Ustedes escuchan atentamente. (You all listen attentively.)
Es importante que ustedes escuchen atentamente. (It’s important that you all listen attentively.)
The first sentence is in the indicative present tense and states a simple fact. The second sentence is less certain — they should listen attentively because it’s important, but whether they actually do so is up in the air. The second sentence therefore requires the subjunctive. Take a look at another pair of sentences:
Él duerme hasta las diez. (He sleeps until ten o’clock.)
Su padre está enojado que él duerma hasta las diez. (His father is angry that he sleeps until ten o’clock.)
Again, the first sentence (the indicative sentence) deals in facts: He sleeps until ten. Period. The second sentence presents the father’s emotions about the situation, so the sentence demands the subjunctive.