Forming nouns from verbs (-us, -os)

Turning Actions into Concepts (-us / -ys)

Finnish turns verbs into abstract concepts, actions, or processes using the suffixes -us or -ys added to the verb stem.

For example, kehittyä (to develop) becomes kehitys (development), and saavuttaa (to achieve) becomes saavutus (achievement).

Other common nouns formed this way include ajatus (thought, from ajatella) and korjaus (repair, from korjata).

Expressing Results (-os / -ös)

While -us / -ys often focuses on the process, the suffixes -os / -ös typically express the concrete result of an action.

For instance, kääntää (to translate) becomes käännös (a completed translation).

Using Grammatical Cases with These Nouns

Nouns ending in -us / -ys and -os / -ös follow a specific pattern when taking case endings:

• To form the partitive case, add -ta / -tä directly to the basic noun (e.g., käännös becomes käännöstä).
• For most other cases (like the genitive, inessive, or elative), the final -s changes to -kse- before the case suffix. For example, ajatus becomes ajatuksesta (about the thought).

Here is how these stem changes look in action: