Learn Hardcore Turkish: Toplantıyı başlatmak üzere herkes yerine oturuyor. - Everyone is taking a seat in order to start the meeting.

Because başlatmak is transitive and takes a direct object. Specific/definite direct objects are marked with the accusative -(y)ı/-(y)i/-(y)u/-(y)ü. Here, the last vowel of toplantı is ı, so you get toplantı-yı (the -y- is a buffer). Without the accusative, it would sound like an unspecific “a meeting,” which is not intended here.

What’s the difference between başlamak and başlatmak, and why is başlatmak used?

başlamak is intransitive: “to begin.” The thing begun is marked with dative: Toplantıya başlamak.
başlatmak is causative/transitive: “to start [something].” It takes an accusative object: Toplantıyı başlatmak. In the sentence, the idea is “start the meeting,” hence the transitive başlatmak.

What does the -mak/-mek üzere construction mean here?

It forms an adverbial of purpose, roughly “in order to.” So Toplantıyı başlatmak üzere = “in order to start the meeting.” The same pattern can also mean “on the verge of/about to” in other contexts (e.g., Toplantı başlamak üzere = “The meeting is about to start”).

Can I use için instead of üzere? Any nuance difference?

Yes: Toplantıyı başlatmak için herkes yerine oturuyor is fine. Üzere is more formal and often suggests an arranged, imminent action (common in announcements), while için is the neutral, everyday way to express purpose.

Who is understood to be the subject of başlatmak in Toplantıyı başlatmak üzere?

By default, the subject of the -mek/-mak üzere clause is the same as the main clause subject. Here it’s herkes. If you need a different subject, you typically switch to a finite clause with için or diye (e.g., “They notified the chair so that he would start the meeting”: Toplantıyı başlatması için başkana haber verdiler).

Why is the verb singular (oturuyor) after herkes? Shouldn’t it be plural (oturuyorlar)?

Herkes (“everyone”) is grammatically singular in Turkish, so the verb is singular: Herkes … oturuyor. Using plural agreement (oturuyorlar) after herkes is colloquial and generally considered nonstandard. If you want a noun that more naturally takes plural agreement, use hepsi: Hepsi yerlerine oturuyorlar.

Should it be yerine or yerlerine?

Both occur. Prescriptive grammar prefers singular agreement with herkes, hence herkes yerine (“to his/her seat”). In everyday speech, herkes yerlerine (“to their seats”) is also very common and sounds natural. To sidestep the singular/plural feel, you can say Herkes kendi yerine.

What exactly is yerine morphologically, and why dative case?

Yer (place) + 3rd person possessive -i → yeri (his/her place) + dative -ne → yerine (“to his/her place”). You use dative because the motion is “to” a place. Contrast: yerinde (locative “in/at his/her place”) would describe being located there, not moving there.

Does yerine also mean “instead of”? Is there any ambiguity here?

Yes, X’in yerine means “instead of X.” That’s a separate, fixed postposition use. There’s no ambiguity here because there’s no genitive-marked noun before yerine; here it clearly means “to (one’s) place/seat.”

Does oturuyor mean “is sitting” or “is sitting down” here?

With yerine, oturmak is understood as “to sit down/take a seat,” and oturuyor is present progressive: “is taking (their) seats now.” For the habitual “sits,” you’d use the aorist (oturur). For residence (“live”), it’s used with a location: Ankara’da oturuyor.

Why is it oturuyor (with -uyor) and not something like oturyor?

The progressive suffix is -yor. When the verb stem ends in a consonant, a vowel matching the last stem vowel is inserted: a/ı → ı, e/i → i, o/u → u, ö/ü → ü. Otur- has last vowel u, so you get otur-uyor → oturuyor.

Can I change the word order?

Yes. Common variants:

Toplantıyı başlatmak üzere herkes yerine oturuyor (as given).
Herkes, toplantıyı başlatmak üzere, yerine oturuyor.
Herkes toplantıyı başlatmak üzere yerine oturuyor. Turkish is flexible, but keep the -mek üzere phrase close to the clause it modifies for clarity.

Is a comma needed after the initial -mek üzere phrase?

Optional. Many writers put a comma after a fronted adverbial: Toplantıyı başlatmak üzere, herkes… Without the comma is also acceptable, especially if the phrase is short and the sentence is clear.

Could we say Toplantı başlamak üzere instead? How does that change the meaning?

Toplantı başlamak üzere means “The meeting is about to start (now),” focusing on the meeting’s imminence. The original sentence focuses on people’s action and its purpose. You could use both together: Toplantı başlamak üzere; herkes yerine oturuyor.

Are there natural synonyms for yerine oturmak?

Yes: yerini almak or yerine geçmek both mean “to take one’s seat.” For example, Herkes yerini alıyor is a very natural alternative here.