Both "Il bicchiere è tuo" and "È il tuo bicchiere" are both valid sentences, but they're subtly different due to their different grammatical structures. They are not perfectly interchangeable, especially in translation lessons.
"Il bicchiere è tuo" is "The glass is yours", where "the glass" is the noun phrase as the subject and "yours" is the possessive pronoun as the subject complement.
"È il tuo bicchiere" is "It is your glass", where in English there's a pronoun as the subject and in Italian the subject is implicit, and "il tuo bicchiere" is the noun phrase as the subject complement.
I'm going to assume you're an English speaker asking the question in Italian.
When it's the possessive adjective (my thing, your thing, her thing, etc) you must always include the definite article, except with singular family members:
la mia gonna
le mie gonne
i miei fratelli
When it's the possessive pronoun (mine, yours, hers, etc), whether you include the definite article or not subtly changes the focus:
- "La gatta è la mia" means "The CAT (and not something else) is mine."
- "La gatta è mia" means "The cat is MINE (and not someone else's)."
Great explanation!!! Without these inputs, it's difficult to understand. The reason why I've accumulated hundreds of "words" in Italian over the years but was unable to understand or create a sentence. Grazie Mille Now I just have to spend a few days playing out those scenarios till it's embedded in my brain.
No. "X is yours" and "It is your X" might be broadly similar, but they are not universally interchangeable. At the very least, they have different grammatical structures and Duolingo is trying to teach us both grammar and vocabulary.
Also, best practice when translating is to stay as close as possible to the source, as far as grammar and idiom allow.