Learn Finnish: Kun nukuin teltassa, yö oli kylmempi. - When I slept in the tent, the night was colder.

To form the comparative, we add the suffix -mpi. However, before adding it, the final vowel -a or -ä of the adjective stem changes to an -e. So, the stem kylmä- becomes kylme-, and adding the suffix gives us kylmempi.

Why does teltassa only have one t before the a, if the dictionary word for tent is teltta?

This is because of consonant gradation. The base word is teltta, which has the strong consonant combination -ltt-. When we add a closed ending like the 'in' suffix -ssa, the -ltt- weakens to -lt-, giving us the stem telta- and the final word teltassa.

Why doesn't the sentence say Kun minä nukuin?

In Finnish, the first-person pronouns (minä for 'I' and me for 'we') and second-person pronouns (sinä, te) are often left out. The -n ending on the verb nukuin (I slept) already makes it perfectly clear who is doing the action.

How do we get the past tense form nukuin from the basic verb nukkua (to sleep)?