A clitic is a character or set of characters that is attached to the end of another word to make an enclitic.  Generally speaking, the Persian determiner, i.e., the indefinite enclitic, ی , corresponds with the English ‘a, an, some,’ and ‘several’. It is also a counterpart to یک ‘one’ in Persian. Thus یک کتاب yek ketāb and کتابی ketābi both mean the same: ‘one book, a book.’

In addition to nouns, the indefinite ی only concerns the adjectival construction (and not the possessive construction).

In the plural this ی means ‘some, several’ indefinite things; that is, non-specific plural nouns: کتاب‌هایی means ‘some books, several books.’

.از آنجا کتاب هایی خوب خریدیم
az ānjā ketāb hāyi xub xaridim
“We bought (some) good books there.”

Also, this enclitic ی is mobile; it can be moved and placed either at the end of the noun or the adjective:

Singular:

Plural:

Normally, after a final long /ā/ and long /ū/ an euphonic ی intervenes, and after a long /ī/ and the silent /h/, an alef intervenes (although still the یی form is the best choice); thus:

ناخدای ماهری
nāxodā-ye māheri
ناخدایی ماهر
nāxodā-yi māher
‘a skilled ship captain’

دانشجوی زرنگی
dānešju-ye zerangi
دانشجویی زرنگ
dānešju-yi zerang
‘a hard-working student’

صندلی شکسته‌ای
sandali-ye šekaste-yi
صندلی‌ای شکسته
sandali-yi šekaste
‘a broken chair’

جامهٔ بنفشی
jāme-ye banafši
جامه ای بنفش
jāme-yi banafš
‘a violet shirt/garment’