What is the difference between tu and su?
What is the difference between tu and su and how are they used to show posession?
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tu is used to refer to a possession that belongs or pertains to the person to whom the speaker is directing his speech. Grammatically, it is inflected to match the second person singular (informal).
su is is used to refer to a possession that belongs or pertains to the person to whom the speaker is speaking about and who is not involved in the conversation or to the person to whom the speaker is directing his speech when it refers to the usted(es) form. Grammatically, it is inflected to match the third person (singular or plural) or second person (singular or plural) polite form/usted(es) form.
Both of su and tu are possessive adjectives, and like all possessive adjectives in Spanish, they agree in number with the possession rather than with the possessor. Grammatically, this means that it shows concordance in number with the noun it modifies.
This might be easier to comprehend by way of example (notice that each adjective matches in number the noun it modifies):
?his apples ? sus manzanas (las manzanas de él)
?his apple ? su manzana (la manzana de él)
?her dogs ? sus perros (los perros de ella)
?her dog ? su perro (el perro de ella)
?your three books ? sus tres libros (los tres libros de usted)
?your book ? su libro (el libro de usted)
?your (pl.) papers ? sus papeles (los papeles de ustedes)
?your (pl.) paper ? su papel (el papel de ustedes)
?your cats ? sus gatos (los gatos de ti)
?your cat ? su gato (el gato de ti)
