Learn Hardcore Turkish: Ben bankadan çıkarken seni gördüm. - I saw you while I was leaving the bank.

It makes a “while/as” time clause. çıkarken = “while (someone) is leaving/going out.” It signals that two actions overlap in time. It doesn’t carry tense or person by itself; the main verb gives the tense, and the -ken clause’s subject is assumed to be the same as the main clause’s subject unless another subject is stated.

Why is Ben there if gördüm already means “I saw”?

Turkish is pro‑drop: gördüm (past + 1st person singular) already tells you the subject is “I,” so Ben is optional. Keeping Ben adds emphasis or contrast, like “I (as opposed to someone else) saw you.”

Why bankadan? Which case is that, and why not bankaya?

bankadan is ablative (from/away from): -dan/-den/-tan/-ten. It’s required by verbs of exiting or moving away, e.g., çıkmak “to exit”: “leave the bank” = bankadan çıkmak.
bankaya is dative (to/toward) and fits verbs of entering/going toward, e.g., bankaya girmek “enter the bank,” bankaya gitmek “go to the bank.”

Why is it seni and not sen or sana?

Because görmek “to see” takes a direct object in the accusative.
Mini map for sen:

nominative: sen (you)
accusative (direct object): seni (you)
dative (to you): sana
locative (on/at you): sende
ablative (from you): senden
genitive (your): senin
with: senle/seninle

Can the word order change? Where can seni go, and does that change the meaning?

Turkish is SOV and uses word order for focus. Variants are possible:

Ben bankadan çıkarken seni gördüm (neutral: “While I was leaving the bank, I saw you.”)
Ben seni bankadan çıkarken gördüm (focuses the time/circumstance)
Seni ben bankadan çıkarken gördüm (focuses that it was “you” whom I saw)
Bankadan çıkarken seni gördüm (drops “Ben”; still “I” is clear from -düm) Moving seni doesn’t change who was leaving; the -ken clause still belongs to the subject of the main verb unless another subject is stated.

Could I say çıkıyorken instead of çıkarken? Any nuance?

Yes.

çıkarken (aorist + -ken) is the default “while leaving.”
çıkıyorken (present continuous + -ken) can feel more like “right in the middle of leaving.” Both are correct; the -yorken form is a bit heavier and used when you want to stress the ongoingness.

What exactly is inside gördüm?

gör- (see) + -DI- (simple past) + -m (1st person singular) → gördüm.
Vowel harmony picks the past allomorph: -dı/-di/-du/-dü (and -tı/-ti/-tu/-tü after a voiceless consonant). With gör, you get -dü- → gör-dü-m.

How would I say “after I left the bank, I saw you” instead of “while leaving”?

Use -ince/-ınca/-ünce/-unca for “when/once/after”:
Bankadan çıkınca seni gördüm.
Nuance: -ken = simultaneous; -ince = subsequent (after the leaving was completed).

How do I make it clear that “you” were the one leaving the bank?

State the subject of the -ken clause:

Sen bankadan çıkarken seni gördüm. (You were leaving; I saw you.)
More natural (to avoid repeating “you”):
Sen bankadan çıkarken ben seni gördüm.
Or change the object: Sen bankadan çıkarken onu gördüm.
Without that explicit sen, Turkish assumes the -ken subject is the same as the main subject.

Is the original sentence ambiguous about who was leaving?

No. As written, the default is “While I was leaving … I saw you,” because the -ken clause shares its subject with the main clause, which is “I” (marked by -düm and optionally Ben).

Why isn’t there any article (“a/the”)?

Turkish has no articles. Definiteness is often shown by case marking. Here, seni (accusative) is definite “you,” and bankadan is an adverbial phrase with the ablative—no article needed.

Do I need a buffer consonant like y anywhere (e.g., “bankaydan”)?

No. -dan starts with a consonant, so no buffer is needed. Buffers appear before vowel‑initial suffixes:

banka-ya (to the bank), banka-yı (the bank, acc.), banka-yla (with the bank).

How is çıkarken formed morphologically?

Aorist 3sg of çıkmak is çıkar.
çıkar + ken → çıkarken (“while exiting”).
You can also build it with the present continuous: çıkıyor + ken → çıkıyorken.

Any quick pronunciation/stress tips?

bankadan: ban-ka-DAN (final stress)
çıkarken: çı-KAR-ken (stress on the stem; -ken is light)
seni: se-Nİ (final stress)
gördüm: gör-DÜM (final stress)
Note: ı is the undotted central/back vowel (like a relaxed “uh”); ö/ü are front rounded vowels.

How would this change for polite/plural “you”?

Use sizi (accusative of siz):
Ben bankadan çıkarken sizi gördüm. (polite/plural “you”)

Can I drop seni if context already tells who was seen?

Yes, but then you just have (Ben) bankadan çıkarken gördüm, which is elliptical: “I saw (you/him/her/it) while leaving the bank.” It’s fine if the object is clear from context; otherwise, it sounds incomplete.

Could I say bankadayken seni gördüm? What’s the difference?

Yes. bankada-y-ken = “while (I was) at the bank.”

Bankadayken seni gördüm = I saw you while I was at/in the bank.
Bankadan çıkarken seni gördüm = I saw you while I was leaving the bank.
The first focuses on being located there; the second on the act of exiting.