1. El subjuntivo en cláusulas adjetivas
Capítulo 5
Gramática

2. Clauses…
Sometimes you use an entire clause to describe a noun. This is called an adjective clause.
Do you have a dress which will go with these shoes?
¿Tienes un vestido que vaya con estos zapatos?
The adjective clause (following the “que”) requires subjunctive because we are not sure if a dress out there exists…

3. Más ejemplos… Yes, I have a dress which will be perfect.
Sí tengo un vestido que va perfectamente.
The above is indicative because you DO know of a dress that will work.
I don't see any dress (that) I like.
No veo ningún vestido que me guste.
This is subjunctive because it is negated.

4. Subjuntivo vs. Indicativo
If you don’t have a specific person or thing in mind, or if you are not sure the person exists, you use the subjunctive.
Busco un libro que tenga un artículo sobre los mayas. (not sure if there is a book out there like this, but I’m looking for one)

5. Más ejemplos…
Escoge cualquier cosa que te guste (cualquier=any) this instantly tells you it will be a subjunctive sentence.
Quiero un vestido que sea del color rojo
I want a dress that is red.
¿Conoces un joven que sepa construir casas?
Do you know a young guy that knows how to build homes?

6. Nadie, Nada, or Ninguno(a)
You also use the subjunctive in an adjective clause when it describes a negative word such as nadie, nada or ninguno(a)
No hay nadie que conozca los símbolos aztecas.
There is no one who knows the aztec symbols.

7. The past…
To refer to something or someone unknown in the past, you can use the present perfect subjunctive.
Busco una joven que haya estudiado computación.
I am looking for a young woman that has studied computer science.
No hay nadie que haya visto un extraterrestre.
There is no one that has seen an alien.

8. Subjunctive examples with unknown nouns (Antecedente)
Hay algo aquí que ______________?
Is there anything here you like?
Quiero leer un libro que _________ todo eso. I want to read a book which explains all that.
Conoces a alguien que ______ cerca de aquí? Do you know anyone who lives nearby?
Buscamos una criada que ________ español. We're looking for a maid who speaks Spanish.