perusteellisista

Perusteellisista is the elative plural form of the Finnish adjective perusteellinen, meaning thorough, careful or well-founded. It is used to describe a plural noun in the elative case, often to indicate that something comes from or is based on thorough or well-founded sources. For example, perusteellisista tutkimuksista translates to “from thorough studies.” In longer phrases the noun would typically appear in the elative plural as well, such as perusteellisista tutkimuksista ja lähteistä, meaning “from thorough studies and sources.”

As a grammatical inflection, perusteellinen forms its elative plural as perusteellisista when describing a plural noun in the elative case. This form is not a standalone lexical entry; rather, it reflects Finnish inflection where adjectives agree with the noun in number and case. The root is peruste- from peruste (basis, foundation) plus the adjectival suffix -ellinen, producing perusteellinen and its various declined forms.

Usage in Finnish is most common in formal, academic, or analytical writing where authors wish to emphasize that claims, conclusions, or data are grounded in careful analysis or solid evidence. The elative form, in particular, highlights sourcing from or deriving information from whence the thorough materials come.

Related forms include the base adjective perusteellinen (nominative plural: perusteelliset), its genitive plural form perusteellisten, and the adverbial form perusteellisesti. In context, Finnish speakers also use synonyms such as huolellinen or systemaattinen to convey similar meanings, though tone and nuance may differ.

See also: perusteellinen, elatiivia (Finnish case systems), huolellinen, perusteellisesti.