A noun and the words that modify it, form a group together, which is called a noun phrase in linguistics. For example, “those houses” is a noun phrase consisting of a demonstrative adjective (those) and a noun (houses) as its head. The noun phrase “these old houses” consists of a demonstrative adjective (these), an attributive adjective (old) and the head “houses”. Sometimes a noun phrase is just a noun without any types of modifiers. For example, in the sentence “Exercise is good for health”, the noun phrase is “exercise”. Therefore, it can be said that a noun phrase consists of a noun and zero or more dependents.

It is important to know about the concept of grammatical phrases and noun phrases in particular, because in Persian, certain grammatical elements are placed at the end of a noun phrase rather than to its head (i.e. to the noun). For example, the indefinite article (-i) comes at the end of a noun phrase.

When a noun phrase consists of only a noun, “the end of a noun phrase” means after the noun because the noun phrase has only one member:

a book
a man

However, when a noun phrase consists of a noun and one or modifiers, it becomes obvious why the grammatical rule says the indefinite article comes at the end of noun phrases:

کتاب خوبی
[ketâb-e khub]-i
a good book
کتاب خوب و آموزنده‌ای
[ketâb-e khub o âmuzande]-i
a good and informative book

In English, the indefinite article is added to the beginning of a noun phrase whereas in Persian, it is added to the end.