Learn Finnish: Kun haastattelin ehdokasta, arvioin hänen soveltuvuuttaan. - When I interviewed the candidate, I assessed his suitability.

Both haastatella (to interview) and arvioida (to assess) are partitive verbs. They describe ongoing processes or subjective evaluations rather than completed physical transformations, so they require their objects to be in the partitive case.

Does arvioin mean "I assess" or "I assessed"? How can you tell?

It means "I assessed" in this sentence. For the verb arvioida, the first-person present (minä arvioin) and past (minä arvioin) look exactly the same because the past tense marker -i- merges with the stem. You have to rely on the surrounding context. Since the first clause uses the past tense verb haastattelin, we know arvioin is also past tense.

How is the word soveltuvuuttaan formed, and why does it end in -an instead of -nsa?

The root noun is soveltuvuus (suitability). First, it takes the partitive ending to become soveltuvuutta because of the verb arvioida. Then, the third-person possessive suffix for "his/her" is added. When a case ending finishes with a short vowel, this suffix is typically formed by lengthening that final vowel and adding -n, resulting in soveltuvuuttaan. The alternative soveltuvuuttansa is technically correct but less common.

If we wanted to say what the candidate is suitable , how would be used?