Learn Hardcore Turkish: Bize yazman iyi oldu; planı netleştirdik. - It was good that you wrote to us; we clarified the plan.

yaz (write) + -ma (verbal noun/nominalizer) + -n (2nd person singular possessive) → yazman = “your writing.” This whole noun phrase acts as the subject of iyi oldu. You can make the subject explicit with a genitive:
Senin bize yazman (iyi oldu).

Why is there no senin before yazman? Is Senin bize yazman iyi oldu also correct?

Yes, it’s correct. Turkish often drops the genitive pronoun when the possessive suffix already shows the subject. Adding senin emphasizes or clarifies who did the writing:

Without emphasis: Bize yazman iyi oldu.
With emphasis/clarity: Senin bize yazman iyi oldu.

Why not just say yazdın instead of yazman?

yazdın is a finite verb (“you wrote”) and can’t directly serve as a noun phrase subject of iyi oldu. The structure here evaluates an action as a thing: “your writing (to us) was good.” If you want a finite-clause alternative with similar meaning, use:

İyi ki yazdın (more emotional: “thank goodness you wrote”),
or keep the nominalized structure: (Senin) bize yazman iyi oldu.

What’s the difference between yazman and yazdığın?

Both are nominalizations but with different suffixes and nuance:

yazman = yaz
- -ma (nominalizer) + -n (2sg poss): often evaluates the act in general and is very idiomatic with adjectives like iyi/kötü.
yazdığın = yaz
- -dık (nominalizer) + -ın (2sg poss) → consonant softening: yazdığın. This often feels a bit more event-specific (“the fact that you wrote/what you wrote”). In this sentence, both can work, but yazman is the most natural.

What does iyi oldu add? Could I say iyi instead?

iyi oldu uses past olmak (“it turned out well / it was good [in the end]”). Saying just iyi would be a present-time, more general evaluation (“it is good”), not tied to a completed past result. Compare:

… iyi oldu → outcome/result in the past.
… iyi → a general or current judgment.

Can I use İyi ki instead: İyi ki bize yazdın?

Yes, but the tone shifts. İyi ki expresses relief/gratitude (“thank goodness”), more emotional. … iyi oldu is more neutral and often links to a concrete outcome, as in the second clause.

Why does planı take the accusative -ı?

Because it’s a definite/specific direct object (“the plan”). In Turkish, definite objects take accusative:

Definite: planı netleştirdik.
Indefinite: bir plan netleştirdik (“we clarified a plan”). A bare plan netleştirdik sounds odd; use bir when it’s indefinite.

What is inside netleştirdik morphologically?

net (clear/precise)
- -leş- (become X) → netleş- “to become clear”
- -tir- (causative: make X become) → netleştir- “to clarify”
- -di (past) + -k (1st person plural) → netleştirdik = “we clarified.”
  Note the past marker appears as -di (not -ti) because it follows a voiced consonant.

How do we know it means “we” without biz?

The verb ending shows the subject. -k on a past-tense verb is 1st person plural:

netleştirdim (I),
netleştirdik (we),
netleştirdiniz (you pl./polite), etc.
Turkish usually drops subject pronouns unless emphasizing.

Is the word order fixed? Could I say Yazman bize iyi oldu?

Word order is flexible. Bize yazman iyi oldu is the neutral flow here, but:

Yazman bize iyi oldu puts slight emphasis on the act (yazman).
Bize can move around for emphasis, but keep the nominalized subject near iyi oldu for naturalness.

How would I make this polite/plural “you”?

Use the 2nd person plural possessive on the nominalization:

(Sizin) bize yazmanız iyi oldu; planı netleştirdik.
You can add sizin for emphasis/clarity, just like senin in the singular.

How do I negate or ask a question with this structure?

Negation (of the writing): Bize yazmaman iyi olmadı/iyi değildi.
Yes–no question: Bize yazman iyi oldu mu?
The question particle mi/mı/mü/mu is separate and follows vowel harmony.

Why a semicolon here? Could I use something else?

The semicolon links two closely related independent clauses. You could also use:

a comma plus a linking adverb: …, böylece/bu sayede planı netleştirdik.
a period: two separate sentences. Each choice tweaks the flow and emphasis slightly; the meaning stays intact.

Could I say İyi oldu ki… here?

İyi oldu ki is a set phrase meaning roughly “it was good that…,” but it typically introduces the reason right after it (e.g., İyi oldu ki geldin). In your sentence, you’re first evaluating the action and then stating a result; a semicolon or böylece/bu sayede is more natural than … iyi oldu ki, planı ….

Why not bize yazmak instead of bize yazman?

yazmak is the bare infinitive/nominal form and doesn’t indicate who is doing the action. In this pattern, the subject of the nominalized clause must be marked:

Generic: Bize yazmak iyi (general statement about writing to us).
Specific: (Senin) bize yazman iyi oldu (your writing to us, this time, turned out well).

Is there any ambiguity with yazman meaning “your scribe/clerk”?

In modern usage, yazman as “clerk/secretary” is rare and context-dependent. Here, the presence of bize and iyi oldu clearly signals the verbal-noun reading (“your writing”), so there’s no ambiguity.