Learn Finnish: Varoitamme teitä tästä kemikaalista. - We are warning you about this chemical.

The verb varoittaa (to warn) dictates that the thing you are warning someone about must be in the elative case (-sta/-stä). While English uses the preposition "about", you can think of the Finnish logic as the warning coming out of the source of danger. Notice that the demonstrative pronoun tämä (this) must agree in case with the noun it modifies, which is why it changes to tästä.

Why is the person being warned (teitä) in the partitive case?

Varoittaa requires a partitive object for the person receiving the warning. In Finnish, warning someone is considered an irresultative action, meaning it is an ongoing action without a definitive endpoint or physically completed result. Therefore, the pronoun te becomes teitä.

Could teitä refer to just one person in this sentence?

Yes! Teitä is the partitive form of te. While it is usually the plural "you" (warning a group of people), it is also used for the polite, formal singular "you" (warning one person respectfully, a practice known as teitittely).

What is the difference between the verbs varoittaa and varoa?