Perusteltuun

Perusteltuun is the illative singular form of the Finnish adjective perusteltu, meaning well-founded or justified. It is used to modify a noun in the illative case, indicating movement toward or reference to something that is justified or substantiated. For example: Perusteltuun väitteeseen on vastattava.

Grammatically, perusteltu is derived from the verb perustella (to justify). The illative singular suffix is -uun, producing perusteltuun when the head noun is in illative form (as in väitteeseen, ratkaisuun, argumenttiin). The corresponding nominative singular is perusteltu, and the partitive is perusteltua. In the plural, illative forms include perusteltuihin and nouns in illative plural such as väitteisiin or ratkaisuihin.

Usage notes: Perusteltuun is common in formal, academic, and legal writing, where arguments or claims are described as well-founded. It typically appears in phrases where the noun it modifies is in illative (into/to) case, e.g., “perusteltuun väitteeseen,” “perusteltuihin väitteisiin,” or “perusteltuun argumenttiin.” The word functions as a descriptive quality attached to the noun rather than as an independent concept.

Etymology and related forms: Perusteltu comes from perustella (to justify) with the suffix -tu to form a participial adjective meaning justified. Related forms include perusteltu (nominative singular), perusteltua (partitive), and the various illative/plural forms like perustelluihin, perusteltuihin väitteisiin.

See also: perustelu, peruste, perustella, perusteltu väite.