The relationship between the two languages Farsi and Arabic should be studied in three levels: the influence of Arabic on Farsi, Farsi on Arabic, and comparative literature. This article, Which is a study of the first level, shows that in Sasanid period (pagan Arab), Arab language borrowed about 105 recognized Farsi vocabularies with their meaning. During the first four Islamic centuries, the number of borrowed Farsi vocahularies in Arabic language excedingly grew up to 2000 to 2500 words. In addition to these vocabularies, Iranian culture penetrated into Arah world to a great extend and thus led to a great culture which should he called "Islamic Culture" not "Arabic culture".
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