Learn Finnish: En ollut menettänyt rahaa, koska en ollut olettanut mitään. - I had not lost money, because I had not assumed anything.

To form the pluperfect active negative (I had not done something), you need three parts: the negative verb (en), the past participle of the verb to be (ollut), and the past participle of the main verb (menettänyt or olettanut).

Why is the word for money, rahaa, in the partitive case here?

In Finnish, the object of a negative sentence must almost always be in the partitive case. Even if this sentence were positive, rahaa would still be partitive because money is an uncountable mass noun.

Why do we use mitään for 'anything' instead of jotain?

Mitään is the partitive form of mikään, which is used in negative sentences. Because the verb is negated (en ollut olettanut), Finnish requires this negative pronoun, whereas English uses 'anything'. Using jotain (something) would sound unnatural here.

Could I use hävinnyt instead of menettänyt to mean 'lost' here?

It wouldn't sound right. Menettää means to lose something abstractly, like losing money in a bad investment, losing a right, or losing a loved one. Hävitä is used when you physically misplace a concrete object (like your keys) or when you lose a game.