How do you know when it is bigger/biggest? It seems that this is inconsistent in Duolingo, but I thought both were correct.
Comparative is formed with -τερος or πιο+Adjective. Superlative is definite article+comparative (or with -τατος, but it's meaning is more "too much"). So πχ όμορφος comparative: ομορφότερος-πιο όμορφος superlative: ο ομορφότερος- ο πιο όμορφος- ομορφότατος (which means too beautiful)
The superlative with -τατος (ομορφότατος) doesn't have a negative meaning ("too beautiful"), it just means very beautiful, most beautiful.
why then the translation accepts the greatest, but does not accept the biggest?