Learn Finnish: Juontaja vilkutti tytölle, innokkaalle ihailijalle. - The host waved to the girl, an eager admirer.

This is an example of an apposition, a phrase that renames or further describes the noun right before it (tytölle). In formal Finnish, the apposition must match the case of its head noun. Because tytölle is in the allative case, the entire descriptive phrase innokkaalle ihailijalle must also take the allative ending.

Does the verb vilkuttaa always require the allative case for the recipient?

Yes, vilkuttaa (to wave) takes the allative case (-lle) for the person being waved at. This makes sense because the allative often expresses an action directed to or toward someone, much like the English preposition to.

How does the base adjective innokas turn into innokkaalle?

Words ending in -kas or -käs have stems that end in a double vowel, and they undergo reverse consonant gradation (weak to strong). The weak single k in innokas strengthens to a double kk, and the stem becomes innokkaa-. The allative suffix -lle is then added to this stem, resulting in innokkaalle.

How is the noun ihailija built from its root verb?

It comes from the verb ihailla (to admire). By taking the verb stem ihaili- and adding the agent suffix -ja, you get ihailija (admirer). This suffix works just like -er in English to describe the person performing an action.