Learn Hardcore Turkish: Ben dün gece kitap okurken kardeşim odasında piyano çalıyordu; o melodi beni sakinleştiriyordu. - Last night, while I was reading a book, my sibling was playing the piano in his room; that melody was calming me.

In Turkish the subject pronoun is usually optional because the verb ending already shows who is acting. Ben (I) is added here for emphasis or clarity—perhaps to contrast your action with your brother’s. You can drop it without changing the meaning:
• Dün gece kitap okurken…

What does the -ken suffix in okurken do?

The suffix -ken attaches to a verb to mean “while …ing.” Here okur- is the present stem of okumak (to read), so okurken = “while reading.” It introduces a simultaneous action with the main clause.

Why is çalıyordu used instead of çalıyor or çalacaktı?

Çalıyordu is the past continuous form (“was playing”), built from the root çal- + progressive -ıyor + past -du.
• çalıyor = “is playing” (present continuous)
• çalacaktı = “was going to play” (future-in-the-past)
We use çalıyordu because the brother’s piano playing was ongoing at that past moment (“while I was reading”).

In kardeşim odasında, why do we say odasında and not just odada? How do we form that possessor + locative?

To specify “in his/her room,” Turkish uses a possessive suffix on the noun before the locative. The steps are:
1) oda (room)
2) + 3rd-person possessor -sı ⇒ odası (“his/her room”)
3) + locative -nda ⇒ odasında (“in his/her room”)
If you said kardeşim odada, it would mean “my brother was playing piano in the room,” but you wouldn’t explicitly mark whose room it is.

What is the function of o in o melodi? Is it necessary?

Here o is a demonstrative pronoun meaning “that.” O melodi = “that melody.” It can point back to the piano tune just mentioned. You can omit o and say Melodi beni sakinleştiriyordu, but using o highlights or contrasts that specific melody.

How is sakinleştiriyordu built up? Can you break down its components?

Sakinleştiriyordu = “was calming (me).” Breakdown:
• sakinleştir- = causative of sakinleş- (to become calm) ⇒ “make calm”
• -iyor = progressive aspect (“is/was …ing”)
• -du = past tense marker
Because yor + du contract to yordu, you get sakinleştiriyordu. The object beni (“me”) shows who is being calmed.

What’s the difference between dün gece and geçen gece? Can both mean “last night”?

Yes, both can translate as “last night,” but:
• dün gece is more direct (“yesterday night”).
• geçen gece literally means “the night that passed” and can also mean “the other night” (a few nights ago).
In everyday speech, dün gece is the most unambiguous for “last night.”

Why is there a semicolon between the two clauses instead of a comma or just using ve?

Turkish punctuation allows semicolons to link closely related but distinct clauses. You could replace it with a comma:
• …, kardeşim odasında piyano çalıyordu, o melodi beni sakinleştiriyordu.
Using ve (“and”) would make it more of a simple list of actions, whereas the semicolon here gives each clause its own weight and shows a closer causal or descriptive link.