Only است ast ‘is’ is a full grade verb in this set of pronoun personal endings.

With the exception of است , the rest of the endings are the same in the written and spoken dialects.

In colloquial Persian است becomes –e. Thus, for example, the formal would be خوب است xub ast ‘it is good,’ and the colloquial خوبه xube.

The endings are used in the conjugation of the verb “to be”. They are attached to the end of nouns and adjectives:

من ایرانیَم، ایرانی ام
man irāni-am
‘I am Iranian, I am an Iranian.’

تو خوبی
tó xubi
singular, ‘You are good.’

او دانشجو است
u dānešju ast
‘He/she is a college student.’

ما خوشحالیم
mā xošhāl-im
‘We are happy.’

شما پزشکید
šomā pezešk-id
plural and formal, ‘You are a physician.’

آنها دکترند، دکتر اند
ānhā doctor-and
‘They are physicians.’

ایشان معلّم اند، معلّمند
īšān mo’allem-and
formal ‘He/she is a teacher.’

Notice that in spoken Persian, ایشان does not mean “they” any more. In written materials ایشان could mean “he, she” or “they” and it may be figured out within the context.

When a noun or adjective ends in a vowel, a euphonic [-y-] (which is variably substituted with an alef) intervenes. This does not occur before است:

من اینجا اَم (most common)
من اینجایَم (rarely used)

تو دانشجویی (most common)
دانشجوای (rarely used)

ما خانه ییم (less common)
خانه ایم (more common)

شما تهرانی اید (more common)
تهرانی یید (rarely used)

آنها ایرانی اند (very common)
ایرانیند (rarely used)

Since in any case after the vowels a hiatus, or clash of two vowels, occurs, a Persian speaker is more comfortable using the full grade verb “to be”; that is, the verb هستن:

من اینجا هستم
man injā hastam
“I am here.”
تو دانشجو هستی
to dānešju hasti
“You are a college student.”
ما خانه هستیم
mā xāne hastim
“We are home.”
آیا) شما تهرانی هستید؟)
(āyā) šomā tehrāni hastid?
“Are you from Tehran?”
آنها ایرانی هستند
ānhā irāni hastand
“They are Iranians.”