vokaaleihin
Vokaaleihin is the illative plural form of the Finnish noun vokaali, meaning “vowel.” In Finnish, the illative case expresses motion toward or into something, and in the plural it is formed by taking the plural stem vokaalit and adding the suffix -iin, producing vokaaleihin. Therefore, vokaaleihin translates literally to “to the vowels” or “into the vowels.” The form is standard in linguistic descriptions, phonology, and other contexts where multiple vowels are the referent; it is less common in everyday conversation but perfectly correct in written Finnish when discussing vowel groups or vowel-related processes.
To illustrate the difference, consider the related singular form taloon, meaning “into the house,” and the plural
Finnish inflection features a broad case system, with the illative as one example. The illative plural suffix