Questions & Answers about Tämä järvi on syvempi kuin tuo joki.
How is syvempi formed from the basic adjective?
The basic word for deep is syvä. To make it into the comparative form (deeper), we add the suffix -mpi. However, Finnish spelling rules dictate that an a or ä at the end of a word changes to an e before the -mpi ending. That is why it becomes syvempi instead of syvämpi.
Why are tämä järvi and tuo joki in their basic dictionary forms?
They are the subjects being compared, so they are in the nominative (basic) case. When you compare two things using kuin (than), the second thing (tuo joki) simply copies the grammatical case of the first thing (tämä järvi).
Is there a way to say this without using the word kuin?
Yes! A very common alternative in Finnish is to drop kuin and put the second item into the partitive case. Using that structure, deeper than that river would be tuota jokea syvempi.
Why does the sentence use both tämä and tuo?
This sentence perfectly contrasts two different pointing words (demonstrative pronouns). Tämä means this (referring to the lake close to the speaker), while tuo means that (referring to the river further away, but usually still visible).