 In type II verbs, and "n", "l", "r" or "s" in the stem ending is assimilated to the consonant in the participle ending (as also happens in formation of the first infinitive, although "-s" stem endings take an extra "t" in the first infinitive)

The assimilation causes the final consonant cluster to be strengthened which in turn can weaken a strong cluster if one exists in the stem.See "harjoitella" above.In verbs of types IV, V and VI, the "t" at the end of the stem is assimilated to the "n"