Indefinite and negative pronouns (algo, nada, alguien, nadie)

Things: "Algo" and "Nada"

When investigating a room for clues, you will need words for unspecified things. Use algo to say "something" and nada to say "nothing" (or "anything").

Are you looking for something in the drawer?
¿Buscas algo en el cajón?
There is something strange here.
Hay algo extraño aquí.

Double Negatives: In Spanish, double negatives are perfectly normal—and often required! If a negative word like nada comes after the verb, you must put no before the verb. You are literally saying "I do not see nothing."

I do not see anything in the box.
No veo nada en la caja.
There is nothing behind the mirror.
No hay nada detrás del espejo.

People: "Alguien" and "Nadie"

To talk about unspecified people, use alguien for "someone" and nadie for "no one" or "nobody".

Someone is checking the bag.
Alguien está revisando la bolsa.

The double negative rule applies to nadie as well. If it comes after the verb, you still need to put no before the verb.

There is no one in the office.
No hay nadie en la oficina.

However, if the negative word comes before the verb, it does the job all on its own. You drop the extra no.

No one understands this letter.
Nadie comprende esta carta.