Learn Hardcore Turkish: Yanlış olmasın diye adresi iki kez kontrol ettik. - We checked the address twice so it wouldn’t be wrong.

It introduces a purpose clause: “so that it won’t be wrong / to avoid a mistake.” In other words, it states the reason for the action in the main clause.

What exactly is olmasın grammatically?

Root: ol- (to be, to happen)
Negation: -ma- → olma- (not be)
Optative/subjunctive 3rd person: -sIn → olmasın (“let it not be,” “so that it won’t be”) In purpose clauses with diye, this 3rd-person optative is very common: X olmasın diye = “so that X doesn’t happen.”

Who is the subject of olmasın here?

It’s impersonal/generic. You can understand it as “it” or “there” in English: “so that it won’t be wrong / so that there won’t be a mistake.” The specific thing that could be wrong is inferred from context (the address/result).

What does diye mean and how is it used?

Here diye means “so that / in order that.” It introduces a finite clause (with a verb carrying mood/tense/person). It can also mean “saying/that” in reported speech, but here it marks purpose.

Could I use için instead of diye?

Yes, but the structure changes:

With a verbal noun: Adresin yanlış olmaması için adresi iki kez kontrol ettik.
With an infinitive for our own action: Yanlış yapmamak için adresi iki kez kontrol ettik. Nuance: diye is a bit more colloquial and flexible; için can sound more formal/explicit.

Why is it adresi (with -i)? Why not just adres?

Adresi is the definite accusative: “the address” as a specific, known object. In Turkish, definite direct objects take -(y)i. If you said adres kontrol ettik, it would sound like an indefinite/generic “we checked (an) address,” which is not the intended meaning here.

Does adresi mean “his/her address”?

Not here. adresi can be either:

Accusative of “address” (the address) → our sentence.
3rd‑person possessed noun “his/her address” in the nominative. If you wanted “we checked his/her address” as a direct object, you’d say adresini (possessive + accusative).

Why is kontrol ettik two words and not one?

Because Turkish forms many verbs with a light verb, here etmek (“to do”). The pattern is “noun + etmek”: kontrol etmek = “to check.” In the past, 1st person plural: et- + -ti (past) + -k (we) → ettik. Writing kontroledik is incorrect.

Could I say kontrol yaptık instead?

You might hear it, but the natural collocation is kontrol etmek. Prefer kontrol ettik.

What’s the difference between iki kez, iki kere, and iki defa?

They all mean “twice.”

iki kez: neutral/standard, a bit more formal in some registers
iki kere: very common in speech, colloquial
iki defa: also common; slightly bookish to some ears but fine

Can I move the diye clause to the end?

Yes: Adresi iki kez kontrol ettik, yanlış olmasın diye. A comma is typical when it comes after the main clause.

Could I express it positively, like “to make sure it’s correct”?

Yes: Doğru olsun diye adresi iki kez kontrol ettik. (optative positive olsun = “let it be”)

What if I want to say “We checked whether the address was wrong,” not “to avoid it being wrong”?

Use the -mI diye pattern: Adresi yanlış mı diye kontrol ettik. This means “we checked to see if it was wrong.”

Where is “we” in the Turkish sentence?

It’s encoded in the verb ending -k in ettik. Turkish doesn’t need a separate pronoun biz unless you want emphasis.

Could I aim the purpose at “us,” like “so that we don’t make a mistake”?

Yes: Yanlış yapmayalım diye adresi iki kez kontrol ettik. Here -yalım is 1st‑person plural optative (“let’s not make [a mistake]”).

Why 3rd person in olmasın if we’re the ones acting?

Because the thing that would be “wrong” is not “us,” but the result/the address. Hence an impersonal or 3rd‑person clause fits: [It] not be wrong.

Any nuance difference between yanlış olmasın and yanlışlık olmasın?

yanlış olmasın: “so that it won’t be wrong” (focus on correctness)
yanlışlık olmasın: “so that there won’t be a mistake” (focus on the occurrence of a mistake) Both are fine; the first is slightly more direct for correctness of the address.

What tense is ettik, and would Turkish use a different tense for English “we’ve checked”?

ettik is simple past (-DI past). Turkish often uses this for both “we checked” and “we’ve checked,” depending on context. Continuous past (ediyorduk) or inferential past (etmişiz) would change the meaning.