Learn Finnish: Vanhaa teoriaa ei liene täysin kumottu. - The old theory was probably not completely refuted.

It uses the negative verb ei, the potential connegative of the verb 'to be' (liene), and the passive past participle of the main verb (kumottu). Together, ei liene kumottu expresses that an action probably did not happen or probably has not been completed.

Why is vanhaa teoriaa in the partitive case?

Because it is the object of a negative sentence. The verb kumota (to refute) usually takes a total object, meaning that in a positive passive sentence, the object would be in the nominative case (Vanha teoria lienee kumottu). However, the negative word ei always forces the object into the partitive case (vanhaa teoriaa).

How is the passive past participle kumottu derived from the dictionary form?

The main verb is kumota (to overturn or refute), which is a verb type 4 word. To form its passive past participle, you take the infinitive stem (kumo-) and add the passive ending -ttu.

Is this grammar structure common in everyday spoken Finnish?

Not really. The potential mood is mostly found in formal writing, literature, and news broadcasts. In everyday conversation, a Finn would more likely use a standard passive perfect negative alongside an adverb expressing uncertainty, such as Vanhaa teoriaa ei luultavasti ole täysin kumottu.