The present paper is going to deal with the problem of existence, and quiddity in Shaykh al-Ishraq Suhrawardi's philosophy.' Certainly, among philosophical problems few topics can be found which enjoys as much' importance as" the "topic 'of existence arid quiddity.' Meanwhile,' Shaykh al -Ishraq's viewpoint on this topic is considered different from that of both Ibn Sina arid Mulla Sadra alid has raised a hot debate. 'Whereas in Mulla Sadra's outlook, existence' is fundamentally' real,' in' Shaykh' al", Ishraq’s theory existence is something mentally-posited arid its three technical meanings are abstract ideas. It is noteworthy that in spite of the developments of philosophical arid theological issues, the value of these two concepts not only has not decreased; but they are also, regarded among the most basic, concepts in the modern philosophy as much as the classical' philosophy so that, the understanding of these two basic terms assists in the solution of other philosophical problems: So explaining the origins of the discussion on this topic, and presenting the meanings and usages of the terms as well as bringing example from Shaykh al-lshraq’s phrases, the author attempts to response the question whether the quiddity, which Shaykh al-Ishraq considers as a made thing and luminous reality, is the same as the quiddity, about which Mulla Sadra says: "it has not smelled the fragrance of existence", or whether there has been some confusion between concepts and their instances, and in fact controversies have been verbally rather than based upon content.