Learn Polish: Lekarz jest wdzięczny pacjentce. - The doctor is grateful to the female patient.

The adjective wdzięczny (grateful) requires the person you are grateful to to be in the dative case. Unlike English, which uses the preposition 'to', Polish just changes the ending of the noun to show who receives the gratitude.

How do we get pacjentce from the dictionary form pacjentka?

Feminine nouns ending in -ka change to -ce in the dative singular. The k softens to a c, and the final -a becomes an -e. So, pacjentka becomes pacjentce. You will see this same pattern in words like matka (mother) turning into matce.

Why is the adjective wdzięczny masculine if the patient is female?

Adjectives must match the gender of the noun they describe. Here, wdzięczny describes the subject of the sentence, lekarz (the doctor), which is a masculine noun. If a female doctor were grateful, it would be Lekarka jest wdzięczna pacjentce.

Where is the word for 'to' in this sentence?

It is built right into the noun's ending! The dative case often translates to 'to' or 'for' in English. By changing pacjentka to pacjentce, you are already saying 'to the patient'. Adding an extra preposition here would be incorrect.