Questions & Answers about Mustikka on sininen marja.
Why is the word for blueberry mustikka if the word for blue is sininen?
In Finnish, berry names often use the noun-building suffix -ikka or -ukka. Mustikka actually comes from the word musta (black). This is because the wild Nordic blueberry (the bilberry) is extremely dark and stains your fingers dark purple or black! You'll see the same suffix in other berries like mansikka (strawberry) and puolukka (lingonberry).
If I make this sentence negative ("The blueberry is not a blue berry"), do I change the ending to partitive?
No, it stays exactly the same: Mustikka ei ole sininen marja. Learners often memorize the rule "negative means partitive," but there is an exception: when the word after the verb to be (olla) is a singular, countable noun (like marja), it stays in the basic nominative case even in negative sentences.
How would the adjective and noun change if we made the sentence plural ("Blueberries are blue berries")?
In the plural, the subject becomes mustikat and the verb becomes ovat. The predicative (the description after the verb) must change to the plural partitive case: sinisiä marjoja. So the full plural sentence is: Mustikat ovat sinisiä marjoja.