How do I determine when to use "su" or "tu" to mean "your"?

Question

I'm pretty sure "tu" always means "your". I, however, have seen "su" also used to mean "your" as well as "his/her/their". How do I determine when to use "su" to mean "your"?

Answer 1

Tu casa means your house and is the familiar form used to address or refer to people you know well such as family

eg:''Mamá, acabo de hablar con tus amigos María y Jóse en la oficina de correos''

''Mum, I have just spoken with your friends, Maria and Joseph in the post office''.

Whereas su is the polite form used to show respect when addressing or referring to strangers, older people or those in authority like your boss or others deserving of special esteem.

eg: El gerente del hotel hablando con algunos nuevos huéspedes

''Esperemos que disfruten su estada en nuestro hotel''

Hotel manager talking to some new guests:

=''We hope that you will enjoy your stay in our hotel''

I hope that helps

I nearly forgot to add that su is also a possessive adjective can also mean his or her

Answer 2

The use of "tú" is informal when speaking to someone and saying you.

For example: Tú hablas español. - You speak spanish.

"Su" is normally used as a possesive adjective for the word his or her.

For example: Su libro- Her/His book

(Someone correct me if I am wrong.)

Good answer, remember that tu without a tilde also means "your" and "su" is the usted form. ;) - Dakie, Mar 26, 2011

Oh, I forgot about that. Thanks. - -Christina-, Mar 30, 2011

Answer 3

(Tu libro) means your book in "tú" form whilst (su libro) means your book in usted form which is the one that you would use with people older than you or just to show respect.