Ib Sina bases his philosophical system on the principle of distinction between existence and quiddity. This principle, but, have been criticized by some other philosophers and thinkers in Islamic world. It has been accepted for a long time by many scholars, and, today, it's still accepted, that some of this critics such as Suhrawardi and Ibn Rushd, have misunderstood Avicennian view of this distinction. But, is there really such a misunderstanding? Our response to the question of misunderstanding is that, as to Ibn Rushd, yes he did it, but, as to Suhrawardi, the answer is no he did not. Because Ibn Rushd sees Ibn Sina as a commentator who had misinterpretated Aristotle. While Suhrawardi do not think so. Analyzing Suhrawardi's 'iitibarat aqliyyah'[rational considerations] will show that, understanding basic differences between Aristotle and Ibn Sina and basing himself on the new elements of 'anvar-I ilahiyyah' [metaphysical lights] and 'izafah ishraqiyyah' [illuminative relation] which are the philosophical explanations of the theorem 'iijado-shey min la shey' [existentiating the thing not from something], makes him a different critic of Ibn Sina's philosophy. Ibn Sina himself in some cases had mentioned that he has never aimed external distinction betweet existence and quiddity, which he sees between wall and whiteness. He pruposes metaphysical distinction not external. Suhrawardi was aware of this kind of distinction precisely. Indeed, Suhrawardi's criticism is about metaphysical distinction, not external distinction, though the structure of his specific objections is similar to those which Ibn Sina and Ibn Rush pose against external distinction. This may be why there has been thought of Suhrawardi that he has misunderstood Ibn Sina's distinction between existence and quiddity.