in relative clauses that express desires
relative clause expresses a desire it is to be put in
again is grounded on the basic rule: if something is
not real, an expression of doubt, desire, intent or
fear the subjuntivo
is to be used.
una mujer que sea guapa, rica, amable y joven.
= He looks for a woman that is beautiful,
rich, loveable and young.
The relative clause expresses a wish, a desire.
un coche que no necesite gasolina.
= I need a car that doesn't need any gas.
The relative clause expresses a wish, or better
a comparison: Necesito ese coche, que corre
a 300 km la hora.
= I need the car that goes at 300 km per
It is a fact that I need that car and the
car is a certain, real car.