Learn Turkish: Gala için belirlenen kıyafet kodu çok katı. - The dress code determined for the gala is very strict.

The verb root is belirle- (to determine). We add the passive suffix -n to get belirlen- (to be determined), and then the subject relative participle -en to get belirlenen (that which is determined). It acts as an adjective describing the dress code.

Why does belirle- take -n for the passive instead of -il or -in?

The passive suffix depends on the last letter of the verb root. Because belirle- ends in a vowel, it simply takes -n. Verbs ending in consonants usually take -il (or -ıl / -ul / -ül), except for those ending in 'l' which take -in.

In the phrase belirlenen kıyafet kodu, why do we use the -An participle instead of -DIk?

We use -An because the modified noun (kıyafet kodu) is the subject of the participle clause ('the dress code is determined'). If we used the active form of the verb where someone else was the subject (e.g., 'the dress code that they determined'), we would use -DIk: belirledikleri kıyafet kodu.

Why does kod have a -u at the end in kıyafet kodu?