"The lion is big."
Translation:Lew jest duży.
Should it not be instrumental? Lew Jest Duzym? Sorry I don't have PL keyboard.
Your proposition does not sound that unnatural (although is considered to be erroneous) because one may say: Lew jest dużym kotem - The lion is a big cat. Here we have instrumental because the adjective is linked with „kotem”. If case of „Lew jest duży”, adjective duży should be in the same case as Lew, which is in nominative.
Cool, so its not nominative when has to follow a noun in concordance?
after a form of "być", an adjective takes Nominative, but a noun phrase takes Instrumental.