The rule is simple: you cannot mix back and front vowels in the same non-compound word. Ever. Kaura (oat) is fine. Käyrä (curve) is fine. But Käura ? That’s linguistic blasphemy. Your mouth will be punished.
: The book primarily uses translation exercises to reinforce learning, with a complete answer key located at the back for self-correction. Finn Lectura Usage Tips Finnish Language Learning BOOK REVIEW List - Oppikirjat From Start to Finnish- A Short Course in Finnish
Example: kukka (flower). Nominative: kukka. Genitive: kukan (kk → k). Partitive: kukkaa (back to strong). Why? Finnish linguists shrug. Tradition. The rule is simple: you cannot mix back