Most of the tenses we've encountered so far (the present, past, future) describe
concrete reality- that which is happening, happened, or will happen. The subjunctive
(see subjunctive
conjugations) expresses a reality that isn't concrete- what someone wants
to happen or what might happen, for example.
In the following sentences, the subjunctive is used in the phrases expressing
what someone wants- volition.
In all but a few rare cases, the subjunctive will appear only in subordinate
phrases- phrases introduced by the relative pronoun que. However, just
because a verb is in a subordinate phrase does not mean it must be a subjunctive.
The following subordinate phrase expresses concrete reality.
Beyond querer and me gustaria, volition can be expressed by giving orders,
prohibiting something, or any other way where some desire is expressed.
The subjunctive is also frequently used whenever there is the least bit of
judgement made about something.
Or when emotion is involved...
This is just a quick introduction to the subjunctive, fully understanding all
the nuances requieres a more in
depth study.