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"Their" is an adjective which is often translated as "su", and "theirs" is a pronoun which is often translated as "suyo". Learn more about the difference between "their" and "theirs" below.
their(
thehr
)An adjective is a word that describes a noun (e.g., the big dog).
1. (possessive)
theirs(
thehrz
)A pronoun is a word that stands in for a noun (e.g., she).
1. (possessive)
a. el suyo (M), la suya (F)
(m) means that a noun is masculine. Spanish nouns have a gender, which is either feminine (like la mujer or la luna) or masculine (like el hombre or el sol).
(f) means that a noun is feminine. Spanish nouns have a gender, which is either feminine (like la mujer or la luna) or masculine (like el hombre or el sol).
I have some extra copies here for anyone who has forgotten to bring theirs.Aquí tengo otros ejemplares para los que hayan olvidado traer los suyos.
That's my opinion, but I respect theirs.Esa es mi opinión, pero respeto la suya.
b. el de ellos (M), la de ellos (F)
(m) means that a noun is masculine. Spanish nouns have a gender, which is either feminine (like la mujer or la luna) or masculine (like el hombre or el sol).
(f) means that a noun is feminine. Spanish nouns have a gender, which is either feminine (like la mujer or la luna) or masculine (like el hombre or el sol).
I like the tiles we bought, but theirs are better quality.Me gustan los azulejos que compramos, pero los de ellos son de mejor calidad.
Our swimming pool is smaller than theirs.Nuestra piscina es más pequeña que la de ellos.