Diventa "tu sei americana"

In "tu sei americano", "AMERICANO" is an ADJECTIVE, and in Italian adjectives agree with the nouns (or the pronouns) they refer to. So, if "TU" refers to a woman, the adjective that refers to the pronoun "TU" must be SINGULAR FEMININE, so you have "tu sei americana". Please note that in Italian ADJECTIVES don't begin with a capital letter, even though they refer to a nationality. Of course, if the sentence had been "tu sei un'Americana", in that case "Americana" would have been a NOUN, and you should have written it with a capital letter. There are some ADJECTIVES in Italian which are invariable (or indeclinable, that is they don't agree, they don't change), but there are not many of them. Some examples are some adjectives referred to colors, like VIOLA, ROSA, AMARANTO, ecc. or the adjective ARROSTO: you say POLLI ARROSTO, QUAGLIE ARROSTO, ecc. Adverbs used as adjectives and adjectives used as adverbs are invariable as well.

In Italian, only Adjectives (and articles) decline with their Nouns. -- tu sei *un ragazzo americano -- M-S -- tu sei *una ragazza americana -- F-S -- voi siete dei ragazzi americani -- M+F P -- voi siete delle ragazze americane -- F-P -----------[*EDIT] - and Past Participles of any verb -- tu sei stato in America M-S (= you have been in America) -- tu sei stata in America F-S -- voi siete stati in America M-MF P -- voi siete state in America F P ----------- Actually many Past Participles are used only as Adjectives. If you find an adjective alone (especially in nationalities -- like Americano/a), you should infere that it's an Adjective that has been turned into Noun. -- gli Americani -- MF P -- le Spagnole -- F P In our language, we often play at using anything as a Noun -- something that sounds like "the why and the when", or "the before and the after" -- but only Adjectives (and Articles) can be declined M/F - S/P. Ciao

tu sei americana