An adjective clause (oración subordinada adjetiva) is a subordinate clause that describes a noun or pronoun (antecedent) in the main clause.
Subjunctive vs. Indicative
Use the indicative when the antecedent is known to exist.
Use the subjunctive when the antecedent is unknown or uncertain.
Example:
Antecedent uncertain ➙ Subjunctive: Busco un abogado que sea honrado. (I’m looking for a lawyer who is honest.)
Antecedent certain ➙ Indicative: Conozco a un abogado que es honrado, justo e inteligente. (I know a lawyer who is honest, fair, and smart.)
Negative Pronouns
When the antecedent of an adjective clause is a negative pronoun (nadie, ninguno/a), the subjunctive is used.
Personal 'a'
Do not use the personal a with direct objects that represent hypothetical persons.
Use the personal a before nadie and alguien, even when their existence is uncertain.
Example:
No conozco a nadie que se queje tanto como mi suegra. (I don’t know anyone who complains as much as my mother-in-law.)
Yo conozco a alguien que se queja aún más… ¡la mía! (I know someone who complains even more… mine!)
Questions with Adjective Clauses
The subjunctive is commonly used in questions with adjective clauses when the speaker is trying to find out information about which he or she is uncertain.
If the person who responds knows the information, the indicative is used.
Example:
¿Me recomienda usted un buen restaurante que esté cerca de aquí? (Can you recommend a good restaurant that is nearby?) - Subjunctive
Sí, el restaurante de mi yerno está muy cerca y es excelente. (Yes, my son-in-law’s restaurant is nearby, and it’s excellent.) - Indicative