Minä soitan siskolleni keskiviikkona.

I will call my sister on Wednesday.

Breakdown of Minä soitan siskolleni keskiviikkona.

• minä: I
• minun: my
• soittaa: to call
• sisko: the sister
• keskiviikkona: on Wednesday

Questions & Answers about Minä soitan siskolleni keskiviikkona.

Why is minä included in this sentence, and can it be omitted?

The verb form soitan already tells you that the subject is “I” (first-person singular), so minä is technically redundant. It’s included here for emphasis or clarity. In everyday speech you can simply say Soitan siskolleni keskiviikkona and it still means “I’ll call my sister on Wednesday.”

What exactly does soitan mean here? I’ve seen soittaa used for “to play” an instrument too.

Soittaa is a polysemous verb.

• “To call (on the phone)”: when the object is a person in the allative case (-lle), e.g. soitan äidilleni (“I call my mother”).
• “To play (an instrument)”: when the object is an instrument in the partitive case, e.g. soitan pianoa (“I play the piano”).
  In soitan siskolleni, the allative ending on siskolleni makes it clear you’re calling your sister, not playing her.

Why is siskolleni in this form? What do the endings mean?

sisko is the base word “sister.” It takes two suffixes here:

• -lle (allative case) = “to” or “towards.”
• -ni (possessive suffix) = “my.”
  So siskolleni literally means “to my sister.”

Why is keskiviikkona used instead of just keskiviikko?

To express “on Wednesday” in Finnish you use the adessive case (-na/-nä) on days of the week.

• keskiviikko = “Wednesday” (basic noun)
• keskiviikkona = “on Wednesday” (time expression)

Can I change the word order? For example, Keskiviikkona soitan siskolleni?

Yes. Finnish has fairly free word order, because grammatical relations are shown by cases, not position. Changing order shifts the focus or emphasis:

• Minä soitan siskolleni keskiviikkona. (neutral)
• Keskiviikkona soitan siskolleni. (emphasizes the time)
• Siskolleni soitan keskiviikkona. (emphasizes the recipient)

If I want to mention I’m using the phone, how do I add “with the phone”?

You use puhelin in the adessive case (-lla/-llä) to mean “with/by phone.” For example:
“Minä soitan puhelimella siskolleni keskiviikkona.”
Literally: “I call with the phone to my sister on Wednesday.”