Learn Hardcore Turkish: Ayşe not defterini getirdi, ben ise kalemimi unuttum. - Ayşe brought her notebook, whereas I forgot my pen.

not defter-i = the compound “notebook” (the -i here is the 3rd-person possessive/compound marker used in noun–noun compounds).
- -ni = accusative case, realized as -ni because a buffer n appears between two vowels. So: not defter-i-ni.

Is not defteri actually a possessive like “his/her notebook,” or is it just the word for “notebook”?

Here it’s the standard compound for “notebook.” In Turkish compounds (X + Y-(s)i), the head noun takes the same suffix as 3rd-person possessive. It doesn’t have to mean someone’s personal possession unless context forces that reading.

How do I say “a notebook” vs. “the notebook” vs. “her own notebook” in this structure?

Indefinite object (“a notebook”): Ayşe not defteri getirdi (no accusative).
Definite object (“the notebook”): Ayşe not defterini getirdi (accusative -ni).
Explicitly “her own notebook”: Ayşe kendi not defterini getirdi. Note: Ayşe’nin not defterini getirdi means “(someone) brought Ayşe’s notebook,” not necessarily that Ayşe herself brought it.

Why is ben written at all? Doesn’t unuttum already show “I”?

Turkish is pro-drop, so you could say kalemimi unuttum. Here, ben ise is used for contrastive emphasis (“as for me/whereas I”) and to host the clitic ise. Without it, the contrast feels weaker.

What exactly does ise do? How is it different from de/da?

ise marks contrast/topic: “as for,” “whereas,” “on the other hand.”
de/da means “also/too” (additive, not contrastive). Compare:
Ben ise … = “As for me/Whereas I …”
Ben de … = “I also …”

Can ise attach to other words, not just ben?

Yes. It follows the element you want to contrast:

Subject contrast: Ben ise kalemimi unuttum.
Object contrast: Kalemimi ise unuttum. (contrast the object) You place ise immediately after the contrasted element.

Is kalemimi “ka-le-mi-mi” using the question particle mi?

No. It’s kalem-im-i = “my pen” + accusative. The sequence -mi here comes from the possessive -im plus the accusative -i. The yes/no question particle mi/mı/mu/mü is written separately (e.g., kalemi mi?).

Why is there a buffer n in defterini but not in kalemimi?

After a possessive/compound ending in a vowel (like -i in defteri), adding a vowel-initial suffix (e.g., accusative -i) triggers buffer n: defteri + i → defterini.
kalemim ends with a consonant m, so no buffer is needed: kalemim + i → kalemimi.

What’s the general order of suffixes here?

Stem → (possessive/compound) → case → (others).

not defter-i-ni (compound -i, then accusative -ni)
kalem-im-i (1sg possessive -im, then accusative -i)

Why is it getir-di but unut-tu-m?

Past tense -DI harmonizes and also voices/devoices:

After a voiced sound (r), it stays -di: getir-di.
After a voiceless sound (t), it becomes -ti/tu: unut-tu; add 1sg -m → unuttum.

Is the comma before ben ise required?

It’s standard to separate the two independent clauses with a comma. You could also use ama (“but”) for a stronger contrast: …, ama ben kalemimi unuttum.

Can I change the word order?

Yes, for nuance:

Neutral object–verb: Kalemimi unuttum.
Emphasizing the verb/result: Unuttum kalemimi.
Keeping the contrast on the subject: Ben ise kalemimi unuttum. Turkish word order is flexible; the verb typically comes last, and fronting highlights the fronted element.

Could I write bense instead of ben ise?

Yes. The clitic often fuses in writing and speech:

Ben ise = Bense Both are common; bense feels a bit more compact/stylistic.