Mitä "pakkasta" ja "pilvista" tarvoittavat? Are these words adverbs? And how can I make adverbs from nouns and adjectives? Or should I just learn them by heart? I've searched a little and made a conclusion: I had sentences: On pilvista.(It's cloudy) On sumuista.(It's foggy) On pakkasta. On selkeää. Then I found that these words have their initial forms (Nominatiivi): pilvinen, sumuinen, pakkanen, selkeä. And they're used in these sentences in Partitiivi-case. So why do we use them like that? Is it a special function of Partitiivi?