Learn Finnish: Heräsimme asumattoman saaren rannalla. - We woke up on the shore of the uninhabited island.

The base adjective is asumaton (uninhabited), which ends in the caritive suffix -ton (meaning without). When we inflect words ending in this suffix, the stem changes to the strong grade -ttoma-. Here, we add the genitive ending -n to match the noun it modifies, giving us asumattoman.

What is the root of the word asumaton, and how is it built?

It is derived from the verb asua (to live, to reside). It uses the participle stem asuma- combined with the caritive suffix -ton (without). So it literally translates to without residing, meaning uninhabited.

Why aren't asumattoman and saaren in the adessive case to match rannalla?

Because they don't mean on the uninhabited island directly. The sentence literally translates to on the shore of the uninhabited island. The core location is rannalla (on the shore), and asumattoman saaren is a genitive phrase answering whose shore it is.

Why does the base word ranta become rannalla with a double N?

Adding the adessive ending -lla closes the final syllable of ranta. This triggers consonant gradation, where the strong consonant cluster nt softens to the weak grade nn.