Learn Finnish: Roskakorit on tyhjennetty. - The trash cans have been emptied.

In the Finnish passive, there is no grammatical subject. Roskakorit is actually the object of the sentence. Because the passive has no subject, the auxiliary verb olla stays in the default third-person singular form (on), even when referring to multiple things.

How is the passive past participle tyhjennetty formed from the dictionary verb?

The base verb is tyhjentää (to empty), a Type 1 verb. Its passive present form is tyhjennetään. Notice the consonant gradation from the strong nt to the weak nn. To get the perfect passive participle, drop the -ään and add -ty, giving you tyhjennetty.

Why is the object roskakorit in the nominative (basic) plural rather than the partitive plural?

In passive sentences, a plural object that is completely affected by the action takes the nominative plural form (ending in -t). Because the action of emptying the trash cans is finished, it is a total object, so we use roskakorit instead of the partitive roskakoreja.

How does the verb tyhjentää relate to the Finnish word for empty?

It is derived from the adjective tyhjä (empty). Adding the suffix -ntää creates a transitive verb meaning 'to make something empty'. This is a very common pattern in Finnish for turning adjectives into action verbs.