Es vs. Eres in "What is your favorite book?"
Qué eres tu libro favorito? or Qué es tu libro favorito? or neither?
I'm not quite sure how to phrase "What is your favorite book?" Thank you!
3 Answers
Now that you have given your best effort (but haven't as yet filled out your profile) ahem. I will give you the correct translation.
¿Cuál es tu libro favorito? (or preferido) What is your book favorite?
Adjectives usually follow in Spanish, but can sometimes precede. (But that's whole 'nother can of worms 
)
We use "cuál" before the forms of "ser" for the English "what" when we want information and NOT a definition.
When to use "qué" and when to use "cuál" is a matter that gives English speakers nightmares. I have an article I use in my college classes which I may post here.
Buena suerte.--But please fill in your profile!!!
Pretty good post but you could have begun with "Please".
You can type your sentence in the translator and see what you get. It's located on the home page of the website.
I'm answering to clarify an obvious error in your understanding of the words tú and tu. The first is the personal pronoun for "you singular and familiar" that would be written with the verb form eres = tú eres - you are.
The second tu is the second person singular possessive pronoun "your familar" It would be used in an expression like tu libro = "your book".
You should also use the question word cuál in this sentence because the meaning is "which" meaning "what one of many possible choices" see Daniela's answer it's much better.
Please fill our your profile and I will give you a vote.
Definitely not "eres," as it is the conjugation of "ser" for the familiar second-person singular subject pronoun, "tú." "Tú" is not the subject of your sentence.
Now, would you please go back to your profile page and fill in your level of proficiency in both English and Spanish so people who would like to communicate with you will know the best way to do so? It also helps to know whether you're male or female and even a little something about you, such as your reason for joining Spanishdict or even where you're from and how you spend your time. That last part is optional, but we really, really need to know how fluent you are in English and Spanish.
