Learn Finnish: Koulu tarvitsee kuria sen takia, että koulutus on vakava asia. - The school needs discipline due to the fact that education is a serious matter.

This is the pronoun bridge being taught in this lesson. The postposition takia (because of) requires the word before it to be in the genitive case. To connect it to the että clause, we use the pronoun se as a bridge, putting it in the genitive form sen. It literally translates to 'because of it, that...'.

Why is kuria in the partitive case here instead of the accusative?

Kuri (discipline) is an abstract, uncountable noun here. The verb tarvita (to need) usually takes a total object (in the accusative case) for specific, countable items, but it requires the partitive case for mass nouns and abstract concepts.

What is the exact difference between koulu and koulutus in this sentence?

Koulu refers to the physical institution of the school itself, while koulutus is a broader word meaning the ongoing process of education or training.

Why is there a comma right in the middle of sen takia, että?

In Finnish, a comma is strictly used to separate a main clause from a subordinate clause. Even though sen takia että translates smoothly as 'due to the fact that' or 'because', the että begins a new subordinate clause, so a comma must be placed right before it.