"If"
(sa/se)
We say "if" in Turkish by attaching the suffixes "sa/se" to the verb. "sa/se" can be used with both positive and negative verbs and is attached after the tense suffix. We choose the correct one based on the last vowel before it i.e. in the tense suffix. Onlar is an exception, we attach "sa/se" right at the end.


Last Vowel of verb root▶ a/ı/o/u e/i/ö/ü
Ben -sam -sem
Sen -san -sen
O -sa -se
Biz -sak -sek
Siz -sanız -seniz
Onlar -larsa -lerse
Examples:
In Turkish, "sa/se" is most often used with the present simple tense:

Ben yazarsam - If I write
Sen duyarsan - If you hear
Onlar gelirlerse - If they come
Siz izlerseniz - If you watch

Ben unutmazsam - If I don't forget
Sen istemezsen - If you don't want
O okumazsa - If he/she/it does not read
Biz düşünmezsek - If we don't think

...however, it could be applied to any of the tenses:

Ben gideceksem - If I will go
Sen başladıysan - If you started
Biz koşuyorsak - If we are running
Onlar ödemişlerse - If they paid

Ben görmeyeceksem - If I will not see
Sen bulmadıysan - If you did not find
O beğenmemişse - If he/she/it did not like
Siz kullanmıyorsanız - If you are not using