Learn Finnish: Kun kohtaus alkaa, näyttelijä astuu kohti yleisöä. - When the scene begins, the actor steps towards the audience.

It is because of the word kohti (towards). While many Finnish spatial words use the genitive case, kohti is a preposition that specifically requires the word following it to be in the partitive. The base word is yleisö (audience), which takes an -ä ending to become yleisöä.

Wait, I thought Finnish usually puts direction words after the noun. Why does kohti come before it?

You are right that Finnish uses a lot of postpositions, which come after the noun (like talon edessä - in front of the house). However, kohti is a true preposition, meaning it comes before the noun, just like in English. As a handy rule of thumb: prepositions in Finnish usually take the partitive case, while postpositions usually take the genitive.

Is the word kohtaus related to anything else? It looks familiar.

Yes! Kohtaus comes from the verb kohdata (to meet or to face). Aside from meaning a scene in a play or film, it is also the word for a medical attack or seizure. For example, sydänkohtaus is a heart attack.

Why is there a comma after alkaa?

Finnish has stricter comma rules than English. A dependent clause starting with a conjunction like kun (when), että (that), or koska (because) must almost always be separated from the main part of the sentence by a comma. Here, the comma marks exactly where the kun clause ends.