Learn Hardcore Finnish: Reppuni on kevyt, koska jätin tietokoneen kotiin. - My backpack is light because I left the computer at home.

In Finnish you normally show possession by adding a possessive suffix directly to the noun. Reppuni = reppu (backpack) + -ni (my). You wouldn’t say Minun reppu in everyday speech.

How does the adjective kevyt agree with Reppuni?

After the verb olla (to be), the adjective takes the same case and number as the subject. Here Reppuni is nominative singular, so kevyt is also in the nominative singular form.

Why is tietokoneen in the accusative/genitive case rather than the partitive?

Transitive verbs that denote a completed action take a total object in the accusative/genitive. Because you “left the computer” as a finished action, tietokone takes -en. The partitive (tietokonetta) would suggest an incomplete action or indefinite amount.

What case is kotiin, and why is it used here?

Kotiin is the illative case (adding -in to koti) indicating movement into a place: “into the home.” Since you left the computer at home (i.e. moved it into your home), you use kotiin. If you were describing location at home, you’d say kotona (adessive).

Why is the verb form jätin, and which tense is it?

Jätin is the first-person singular preterite (simple past) of jättää (to leave behind). The -in ending tells us “I did this in the past,” so jätin = “I left (it behind).”

What does koska mean here, and could I use siksi että or kun instead?

Koska means “because” and introduces a reason. Siksi että is a more emphatic/explicit way to say “for the reason that,” but otherwise similar. Kun can also mean “when” or “since,” but using kun for cause can sound ambiguous, so koska is clearer for “because.”

Is the comma before koska required?

Finnish allows some flexibility with commas. Placing a comma before koska is common in writing for clarity, but it’s not a strict rule in simple sentences.

Can I start with the reason clause instead of the main clause?

Yes. Finnish word order is flexible. You can say:
Koska jätin tietokoneen kotiin, reppuni on kevyt.
The meaning remains the same; you just emphasize the reason first.