One of the most important differences between formal and colloquial Persian is in verb conjugation. As you know, in formal Persian, there are two sets of verb conjugation suffixes – one for past verbs and one for present verbs. Three of these suffixes change in colloquial Persian:
1- The suffix “ید”, used both in past and present tenses for second person plural, usually changes into “ین”.
چرا رفتید؟
چرا رفتین؟
چیزی می‌بینید؟
چیزی می‌بینین؟
کمک کنید!
کمک کنین!
وقتی علی رسید شما رفته‌بودید.
وقتی علی رسید شما رفته‌بودین.
نباید با هم دعوا می‌کردید.
نباید با هم دعوا می‌کردین.
امیدوارم تمرین کرده باشید.
امیدوارم تمرین کرده باشین.
Why did you (pl.) go?
Do you (pl.) see anything?
Help! (pl.)
You (pl.) had gone when Ali arrived.
You (pl.) shouldn't have argued with each other.
I hope (literally: I am hopeful) you (pl.) have exercised.
2- The suffix “ند”, used in both past and present tenses for the second person plural, is replaced by “ن”.
کجا رفتند؟
کجا رفتن؟
کِی بر می‌گردند؟
کِی بر می‌گردن؟
بچّه‌ها داشتند بازی می‌کردند.
بچّه‌ها داشتن بازی می‌کردن.
Where did they go?
When will they come back?
The children were playing.
3- The suffix “د”, used for the present simple and a few other tenses, is replaced by “ه” in colloquial Persian.