Learn Finnish: Onko kaapissa manteleita? - Are there almonds in the cabinet?

In Finnish existential clauses, the verb is always locked in the third-person singular (on), regardless of whether the subject is singular or plural. Even though we say "are there" in English, Finnish essentially says "is there in the cabinet some almonds?"

Why is manteleita in the partitive plural instead of the nominative plural (mantelit)?

Existential sentences use the partitive case for the subject when referring to an indefinite, unspecified amount of something (like "some almonds"). If you used the nominative plural (Onko kaapissa mantelit?), the meaning would change to asking about specific, known items: "Are the almonds in the cabinet?"

I thought existential sentences had to start with the location. Why does this one start with the verb?

You are right that a standard existential statement puts the location first (Kaapissa on manteleita). However, forming a yes/no question overrides this rule. The word carrying the question particle (-ko) must always jump to the absolute front of the sentence, pulling the verb on to the beginning.

How exactly is manteleita formed from the base word manteli?