Kość jest twarda.

to be

Breakdown of Kość jest twarda.

• twardy: hard
• kość: the bone

Questions & Answers about Kość jest twarda.

Why is it twarda and not twardy?

Because kość is a feminine singular noun, and Polish adjectives must agree with the noun in gender, number, and case.

So:

• twardy = masculine singular
• twarda = feminine singular
• twarde = neuter singular or some plural uses

Since kość is feminine, the correct form is twarda.

Is kość really feminine even though it doesn’t end in -a?

Yes. In Polish, many feminine nouns end in -a, but not all of them do.
A lot of feminine nouns end in a soft consonant or have the -ść ending, and kość is one of them.

So although it may look unusual at first, kość is grammatically feminine.

What case is kość in here?

It is in the nominative singular.

In Kość jest twarda, the noun kość is the subject of the sentence, so nominative is exactly what you would expect.

The adjective twarda is also in the nominative singular because it is describing the subject through jest.

Why is the adjective in the nominative? Why not something like ?