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"Sí" is a form of "sí", an adverb which is often translated as "yes". "Son sus libros" is a phrase which is often translated as "they're his books". Learn more about the difference between "son sus libros" and "sí" below.
son sus libros(
sohn
soos
lee
-
brohs
)A phrase is a group of words commonly used together (e.g., once upon a time).
a. they're his books (masculine)
¿Son esos los libros de tu hermano? - Sí, son sus libros.Are those your brother's books? - Yes, they're his books.
b. they're her books (feminine)
Esos libros son de Marta. - Si son sus libros, ¿por qué están en tu mochila?Those books are Marta's. - If they're her books, why are they in your backpack?
c. are his books (masculine)
¿Se ha ido ya Pedro? - No creo, esos que hay ahí son sus libros.Has Pedro already left? - I don't think so. Those over there are his books.
d. are her books (feminine)
¿Los libros de Isabel son los que están en esta estantería? - Sí, esos son sus libros.Are Isabel's books the ones on this shelf? - Yes, those are her books.
2. (formal) (second person singular)
A word or phrase used to refer to the second person formal “usted” by their conjugation or implied context (e.g., usted).
a. they're your books
Si son sus libros, lléveselos a su cuarto.If they're your books, take them to your room.
b. are your books
Los que están encima de la mesa son sus libros, ¿verdad?Those on the table are your books, aren't they?
sí(
see
)An adverb is a word that describes a verb, an adjective, or other adverbs (e.g., to run quickly, very tired).
a. yes
¿Quieres ir al cine? - Sí, pero primero hay que comer.Do you want to go to the movies? - Yes, but let's eat first.
2. (emphatic)
a. no direct translation
This refers to an idiomatic word or phrase for which there is no word-for-word translation.
Yo sí quiero acompañarlos a Disney.I do want to go with you to Disney World.
Ella no aprobó, pero yo sí.She didn't pass, but I did.
An interjection is a short utterance that expresses emotion, hesitation, or protest (e.g., Wow!).
A masculine noun is used with masculine articles and adjectives (e.g., el hombre guapo, el sol amarillo).
A pronoun is a word that stands in for a noun (e.g., she).
a. himself (third person singular masculine)
Suele jugar ajedrez con sí mismo.He usually plays chess against himself.
b. herself (third person singular feminine)
¡Se envió una carta a sí misma!She sent a letter to herself!
c. itself (third person singular)
El hilo se está enredando en sí.The string is getting tangled up in itself.
e. yourself (second person singular formal)
Solo desea el bien para sí.You only wish good for yourself.
f. yourselves (second person plural formal)
¡Solo tienen que creer en sí mismos!You just have to believe in yourselves!
