Learn Finnish: Poliisi syyttää miestä, sillä todiste on selkeä. - The police accuse the man, because the evidence is clear.

Yes, you could say ...koska todiste on selkeä. Both mean 'because', but they differ slightly. Sillä is a coordinating conjunction (like 'and' or 'but'), meaning it connects two independent main clauses. Koska is a subordinating conjunction, which introduces a dependent clause. In everyday spoken Finnish, koska is much more common, while sillä sounds a bit more formal or written.

Is the comma before sillä mandatory?

Yes. Because sillä connects two complete, independent clauses (Poliisi syyttää miestä and todiste on selkeä), Finnish grammar rules require a comma between them.

Why is the man in the partitive case (miestä) rather than the accusative?

The verb syyttää (to accuse) is a partitive verb. This means the person or thing you are accusing must always be in the partitive case. It helps to remember that expressing a feeling, attitude, or continuous action directed at someone often triggers the partitive in Finnish.

In English, we say 'the police accuse' as a plural, but the Finnish verb syyttää is singular here. Why?

In English, 'police' is a collective noun usually treated as plural. In Finnish, the institution of the police (poliisi) is grammatically singular, so it takes a singular verb. If you wanted to talk about several individual police officers, you would use the plural noun poliisit alongside the plural verb syyttävät.