Learn Hardcore Finnish: Tämä projekti on tärkein suunnitelmani tänä vuonna. - This project is my most important plan this year.

In Finnish, you form the superlative (“most …”) by adding -in to the strong grade of the adjective stem.
• tärkeä → stem tärkeä- → tärkein (“most important”).
Vowel harmony applies, so ä stays consistent.

Why is suunnitelmani not marked with an extra case ending after the possessive suffix -ni?

After the copula on (“is”), the predicate takes the nominative case.
• suunnitelma (plan) in nominative + -ni (1st person singular possessive) → suunnitelmani (“my plan”).
No further case ending is needed.

What is the function of the suffix -ni in suunnitelmani?

The suffix -ni is the first person singular possessive suffix. It means “my.”
• suunnitelmani = “my plan.”

Why is vuonna used in tänä vuonna, and what case is it?

Vuonna is the ESSIVE case of vuosi (year). The essive is used for time expressions meaning “in/on (a certain time).”
• tänä vuonna = “this year.”

How does tämä become tänä in tänä vuonna?

To match vuonna in the essive, the demonstrative tämä also takes the essive ending.
• tämä → tänä, showing “this” in relation to the time word “year.”

Can the time expression tänä vuonna be placed elsewhere in the sentence?

Yes. Finnish word order is flexible. You can emphasize different elements by moving tänä vuonna to the front:
• Tänä vuonna tämä projekti on tärkein suunnitelmani.
This still means “This project is my most important plan this year.”

What is the difference between tärkeä, tärkeämpi, and tärkein?

They are the three degrees of comparison:
• tärkeä = “important” (positive)
• tärkeämpi = “more important” (comparative, -mpi suffix)
• tärkein = “most important” (superlative, -in suffix)

Why is projekti singular and in the nominative case here?

The sentence refers to one specific project, so projekti is singular. As the subject of the verb on (“is”), it takes the nominative case.