Learn Hardcore Turkish: Postacı erken gelirse kapıyı açmanı istiyorum. - If the mail carrier comes early, I want you to open the door.

aç- = open (verb stem)
-ma = nominalizer (turns the verb into “opening”)
-n = 2nd person singular possessive (“your”)
-ı = accusative (because this whole action is the direct object of istiyorum)

So aç-ma-n-ı literally means “your opening.”

Why is kapıyı in the accusative?

In Turkish, definite direct objects take accusative: -(y)ı/-(y)i/-(y)u/-(y)ü.
Here, kapıyı is the door we have in mind (definite), and it is the object of the verb inside the nominalized clause (aç-).
You can have accusative twice across clause boundaries: inside the nominalized clause (kapıyı as the object of aç-) and on the whole nominalized action (açmanı) as the object of istiyorum.
If you wanted an indefinite object, you would drop the accusative: bir kapı açmanı istiyorum = “I want you to open a door.”

Do I need to say senin (as in senin kapıyı açmanı istiyorum)?

No. The person is already marked by the possessive -n in açmanı. You add senin only for emphasis or disambiguation:

Neutral: kapıyı açmanı istiyorum
Emphatic/contrastive: senin kapıyı açmanı istiyorum (“I want you, not someone else, to open it.”)

How do I say this politely or to more than one person?

Use the siz form (2nd person plural/polite):

kapıyı açmanızı istiyorum = I want you (polite/plural) to open the door. Other persons:
kapıyı açmasını istiyorum = I want him/her to open the door.
kapıyı açmamı istiyorsun = You want me to open the door.

Can I use an imperative instead of istiyorum?

Yes, for a direct request:

Postacı erken gelirse kapıyı aç. (If the postman comes early, open the door.) For polite requests:
Postacı erken gelirse kapıyı açar mısın?
Postacı erken gelirse kapıyı açabilir misin?

What’s the difference between gelirse and gelse?

gelirse = real/likely condition (“if he comes”). It’s the default for “if” in practical conditions.
gelse = hypothetical or wish (“if he were to come / I wish he would come”). Often used with keşke: Keşke gelse.

What exactly is in gelirse morphologically?

gel- = come
-ir = aorist (generic/habitual form)
-se = conditional marker So gel-ir-se ≈ “if he/she comes.” The aorist is the standard base for conditional “if” clauses.

Could I use gelince instead of gelirse?

gelince = “when/once he comes” (time clause)
gelirse = “if he comes” (condition) Your sentence expresses a condition, so gelirse is the best fit. Gelince would sound more like a routine sequence (“when he comes, open the door”).

Is eğer required before gelirse?

No. eğer is optional emphasis:

Eğer postacı erken gelirse, ... and Postacı erken gelirse, ... mean the same. Eğer just adds a bit of focus to the condition.

Is the comma necessary after the conditional clause?

It’s common and helpful but not mandatory. Typical layout:

Postacı erken gelirse, kapıyı açmanı istiyorum. You can also place the conditional clause after the main clause:
Kapıyı açmanı istiyorum, postacı erken gelirse. Both are grammatical; leading with the condition is more natural.

Can I move kapıyı elsewhere?

Yes, Turkish word order is flexible, but keep related words close for clarity. The most natural spot is just before açmanı:

Postacı erken gelirse, kapıyı açmanı istiyorum. Moving kapıyı far away can sound marked or awkward.

Does postacı mean “the postman” or “a postman” without an article?

Turkish has no articles. postacı can be generic or specific depending on context. In this sentence, it’s usually understood as “the postman” (the one who comes to your place). If you need to be very specific: bizim postacı (“our postman”).

What does the suffix -cı in postacı do?

It forms an occupational noun: posta (post/mail) + -cı (“person who does/deals with”) → postacı (“postman, mail carrier”). You see it in many jobs: balıkçı (fisher), şoför doesn’t take it, but bakkal is shopkeeper (lexical).

What’s the nuance between erken and erkenden?

erken = early.
erkenden = quite early / earlier than usual, with a bit more emphasis on earliness. Both work; erkenden can sound stronger or more colloquial.

How do I negate the request?

Negate inside the nominalized verb:

kapıyı açmamanı istiyorum = I want you not to open the door. With the condition:
Postacı erken gelirse kapıyı açmamanı istiyorum.

Why is it istiyorum (present continuous) and not isterim?

istiyorum expresses a current, concrete desire (“I want right now”).
isterim (aorist) is more general, habitual, or sometimes sounds tentative/polite depending on context. For a specific, present request, istiyorum is the default.

Why is there a buffer -y- in kapıyı?

When a vowel-final word takes a vowel-initial suffix, Turkish inserts a buffer consonant to avoid a vowel clash. For many nouns it’s -y-:

kapı + ı → kapıyı Vowel harmony also picks the right vowel: since the last vowel of kapı is ı (back, unrounded), the accusative is -ı. Pronounce the dotless ı like a close central unrounded vowel (similar to the second vowel in English “roses” for many speakers).