A pronoun replaces a noun which has been mentioned previously in a conversation or is obvious from context. An indefinite pronoun refers to nonspecific people or things. Most of these words can also be used as indefinite adjectives when preceding a noun.
Alguien and Algo
Alguien somebody is used in affirmative or interrogative sentences to refer to a person. Algo something is the equivalent pronoun used to refer to a thing.No quiero ofender a alguien o malinterpretar alguna palabra.
I don’t want to offend anyone or misinterpret some word.
The negative form of alguien is nadie no one and the negative form of algo is nada nothing. Notice that Spanish uses double negatives, unlike English.Era medio difícil. Nadie me podía casar, yo no me quería casar con nada, con nadie.
I was somewhat difficult. No one could get me marry off, I didn’t want to marry anything or anyone.
Muchos/muchas many, algunos/algunas some, todos/ todas all are plural indefinite pronouns. In other contexts, they can also be used as adjectives. Here, they are used in place of plural nouns and must agree in gender with that noun. Compare the examples below.¿Cuál es tu platillo mexicano favorito? Uh… hay muchos, pero se me hace que a mí me gusta más el menudo.
Which is your favorite mexican dish? Uh… there are many but I think that I most like menudo.
Cuéntame de tus hijos. ¡Ay! Todos son bien diferentes.
Tell me about your children. Ay! All of them are very different.
Todas mis hermanas tenían una personalidad muy distinta. La mayor… es la más seria de todas.
All of my sisters have a very different personality. The oldest is the most serious of all of them.
Todo is invariable when it functions as the indefinite pronoun meaning everything or all, as in the first sentence below.¿Y las clases se impartían sólo en español? Sí, todo era español.
And the classes were given only in Spanish? Yes, everything was in Spanish.