Este es un correo electrónico que le envié a uno de mis estudiantes y me pareció bueno dejarlo por aquí, por si a alguien le puede servir.
For using the subjunctive mood you need, in first place, a sentence with two
clauses. A clause is an syntactical sequence (syntagm) that has a subject and a
conjugated verb, for example:
(Yo) Pienso (I think). As you notice, Spanish
doesn't really need subject pronouns (though, there are cases when it does use
them), because we can tell who the performer is thanks to the verb ending.
The subjunctive mood is used when you are going
to express what you doubt, feel uncertain about, a hypothetical situation or a
wish in the second clause (the clause that comes after the connector
"que"). The hint to know whether to use indicative or subjunctive is
the information expressed by the verb of the first clause. For example, in the
clause:
Yo sé (I know), your verb (saber) expresses
certainty, right?
Yo sé que tú eres inteligente.
I know (that) you are intelligent. This
(compound) sentence has two clauses, "Yo sé" (I know), which
expresses certainty, and "tú eres inteligente" the FACT (that)
I know (you're intelligent).
I am certain of the FACT that you are
intelligent: "Yo sé que tú eres Valerie". Due to the certainty
expressed by the verb "saber" in the first clause (yo sé), you must
use INDICATIVE mood in the second clause (tú ERES inteligente).
On the other hand, when the verb in your first
clause expresses any doubt, uncertainty, a desire or a wish, you NEED
SUBJUNCTIVE mood for the verb in the second clause.
Espero que seas inteligente.
Espero = I hope. This clause, the first clause,
expresses a wish; thus, the second clause "(Tú) seas inteligente" has
to use the subjunctive mood.
More examples and what I said about the verb
"creer":
"Creer" can be translated to English as
"to believe"; however, in Spanish, its meaning is different. If you
use it in an affirmative clause, the meaning equals "I'm (very/pretty)
sure"
Yo creo que hoy es miércoles. I'm (very/pretty)
sure it is Wednesday.
Nosotros creemos que hace frío. We are
(ver/pretty) sure it is cold.
Ellos creen que tú eres Valerie. They are
(very/pretty) sure you are Valerie.
In contrast, when you use "creer" in a
negative clause, the meaning equals "I'm not sure at all". Therefore,
when you use "no creer" in the first clause, you ALWAYS need
Subjunctive for the verb in the second clause.
No creo que HAGA calor. I'm not sure it is hot at
all.
No creen que seas pesimista. They are not sure at
all that you are pessimistic.
No crees que yo vaya a México. You're not sure at
all that I go to Mexico.
If you say that you do not believe or don't think
(No creo, no pienso),that, the first clause (No creo, no pienso), is the fact.
Whatever it is that you don't believe or don't think is the "unreal,
uncertain" thing; therefore, you must use SUBJUNCTIVE for the verb in the
second clause ( the clause that comes after "que"). Compare:
CREO que el examen ES difícil.
CREO (first clause) que (conector) el examen ES
fácil (second clause).
If you look back at what I previously told you
about creer, you'll see that, since I'm using it in an affirmative
clause, It means "I'm pretty sure"; thus, the second clause (el
examen ES difícil) uses indicative mood.
NO CREO que el examen SEA difícil.
NO CREO (first clause) que (connector) el examen
SEA difícil (second clause in SUBJUNCTIVE mood).
NO PIENSO que tú ESTÉS confundida.
NO PIENSO (first clause) que (connector) tú ESTÉS
confundida (second clause in SUBJUNCTIVE mood).
I hope this can help you. Buena suerte.
