Subjunctive in Adjective Clauses

In Spanish, the verb in a descriptive clause (an adjective clause) can be in the indicative or the subjunctive. Your choice depends entirely on whether the person or thing you're describing is known and specific or unknown and hypothetical.

The Main Rule: Certainty vs. Uncertainty

Think of it like this: are you talking about something real and concrete, or just an idea of something?

1. Use the INDICATIVE for known, specific people or things. If the noun being described (the antecedent) is a specific person or thing that the speaker knows exists, use the indicative. You're just adding a description to something definite.

• Tengo el libro que tiene la respuesta. (I have the book that has the answer. I'm holding a specific book.)
• Conozco a la mujer que habla ruso. (I know the woman who speaks Russian. I have a specific person in mind.)

2. Use the SUBJUNCTIVE for unknown, hypothetical, or non-existent people or things. If the antecedent is indefinite, hypothetical, or if the speaker is unsure of its existence, use the subjunctive. You're describing the qualities you're looking for in something that may or may not exist.

• Busco un libro que tenga la respuesta. (I'm looking for a book that has the answer. I don't know if such a book exists, but this is the quality I want.)
• ¿Hay alguien aquí que hable ruso? (Is there anyone here who speaks Russian? I'm asking about a hypothetical person.)
• No hay nadie que pueda ayudarnos. (There isn't anyone who can help us. The person does not exist.)

Key Triggers for the Subjunctive:

• Indefinite articles: un, una, unos, unas
• Negative words: nadie, ninguno/a, nada
• Verbs of searching/wanting: buscar, necesitar, querer
• Questions asking about existence: ¿Hay alguien que...?, ¿Conoces a alguien que...?