Describing Mass Nouns
In Finnish, mass nouns are uncountable substances like materials, liquids, or powders (for example, iron, sand, and dust). When you describe a mass noun with an adjective after the verb olla (to be), the adjective—the subject complement—must be in the partitive singular.
For example, instead of using the basic nominative form raskas (heavy), you use its partitive form raskasta.
You also use the partitive singular when stating what material or substance a specific object is made of. When a noun acts as the subject complement describing a material, it goes into the partitive.
Whether you are describing the substance with an adjective or identifying its material, the partitive rule applies consistently to uncountable masses.
Abstract Subjects
Abstract concepts and intangible things—like youth, envy, or time—behave the same way as mass nouns. When the subject of your sentence is an abstract idea, the adjective describing it must also be in the partitive singular.
General statements about uncountable necessities, such as water or sleep, follow this exact same pattern.