klainsky is right. "dorosły/dorosła" is mostly an adjective "adult", although it can be also interpreted as a noun. However, despite that, it would feel strange to say something like "Ona jest dorosłą". "Ona jest dorosłą kobietą" works, as it is the noun phrase that gets put into Instrumental, not an adjective on its own. Adjectives stay in Nominative.
Part of the confusion may come from Duolingo's "correct" translation of the Polish past participle/adjective "dorosła" as the English noun "adult". It's tricky, because Polish doesn't seem to have an actual noun equivalent for "adult". The lack of a noun to be declined in the instrumental case might have been clearer had the official answer been a more literal English that also avoids a noun and uses rather an English past participle/adjective: "grown up".
Hi Claire, Going great guns with Polish! Thumbs up! On your question, I think you'd need a direct object (in English terms) to use the instrumental case here, whereby "dorosła" would modify, for example "kobieta" and both would be instrumental (doroslą kobietą). In the sentence under discussion, "dorosła" modifies the subject (again, in English terms) "ty" so it stays nominative. Best from Steve
I't is as Klainsky said: Polish dorosły don't work always like English an adult.
In Polish we have three types of personal nouns with the ending -Y:
- that have gender and have declination like nouns: woźny / woźna - a caretaker; motorniczy / motornicza - motorman
- that have gender and have declination like personal adjectives: chrzestny - a godfather, bezrobotny - an unemployed, dyżurny - duty officer, krewny - a relative, księgowy - an accountant
- that have ONLY masculine form and have declination of masculine personal adjectives: myśliwy - a hunter, gajowy/leśniczy - a forester
Dorosły belongs to the third group - as one word it means only male. For female are two words dorosła kobieta
doktor - doctor (occupation), doktor - male doctor, Pani doktor - female doctor
premier - Prime Minister (occupation), Pani Premier - female PM
Because of this you can say:
Widziałeś tego dorosłego, trochę niepoważnie się zachowuje. - You've seen this adult, he's acting a bit unkindly. Only children would use word dorosły - an adult.
Gdzie się podziali wszyscy dorośli? - Where are all grown up? Plural form dorośli is used commonly (independently from the gender of the subject). It used when there are children and adults together.
But we never say:
tą dorosłą - as a female adult
te dorosłe - as at least two female adult
BTW, "to grow up" is complicated in Polish, because of the aspect and some little details. There is the process (imperfective verb) and the result (perfective verb). It is something like "to grow up", "to mature" and "to ripe" in English.
In Polish we have 3 words that means "to grow up":
to achieve age and development enabling independent living (Pies dorósł - A dog grew up (and it is adult dog now))
to match someone in some respect (idiom: Nie dorasta ci do pięt - He/she can't compare to you.)
to become adult (dorosły) (Wydoroślał - He become an adult.)
to pick up of the features typical of the adult (doroślejszy) (Czy wasze dziecko zbyt szybko nie dorośleje? - Are your child not growing up too soon? compare: Czy wasze dziecko zbyt szybko nie dorasta? - Are your child not growing up too fast?)
to achieve the full development (Ten owoc jest już dojrzały, możesz go zjeść. - This fruit is ripe, you can eat it.)
to become independent in life (Dojrzały człowiek. - A matured man.)
to become ready for specific tasks (Dojrzał do tego. - He is ready to do this task.)
to achieve the appropriate quality as a result of fermentation, chemical reactions, etc. - in the case of raw materials, food preparations (Wino jeszcze nie dojrzało - Wine has not riped yet).
"czy" doesn't exactly mean neither "are" nor "do" (as in the hints), it's just a word that makes it clear that you are asking a real question (as opposed to "What?! You're an adult?! I thought you're 15!").
"jesteś" already has the 'you' information in it, but it doesn't mean that "ty jesteś" suddenly means "you you are". It's just specifying the subject for emphasis.