Detailed & precise study on Qādī Sa‘īd writings represents that every existent’s quiddity in Qādī Sa‘īd’s thought is identical to what by which it is what it is or quiddity in general (al māhiya bil ma‘na al a‘am) & quiddity as whatness has not been his target in arguments. In explanation two problems on external realization of quiddity, that are the problem of creation & the problem of distinction, he declares that every quiddity is created by simple creation of it’s creator & denies every kind of beingexistence for quiddity before creation of it’s creator, as well he names the creation of creator as the just cause of distinction of every existent, so the externality & distinction of quiddities does not need to accident of existence to become existent & also does not need to attributes to become distinct.

One of the innovations of Farabi and Islamic philosophy is the theory of the distinction between existence and quiddity. This view was merely developed in the light of understanding the meaning of the reality of being. Islamic philosophers, particularly Farabi and Ibn Sina, because of their epistemological rupture with Greek tradition, sought to understand being differently from Aristotle and, in a way, abstained from reducing the question of being to the question of the whatness of objects. In addition to a conceptual and logical distinction, Farabi managed to develop and present an ontological distinction in the field of philosophy. Ibn Sina expanded it so vastly that some might consider this theory as one of his own philosophical achievements. After the problem of the evidence and principliality of existence, the quality of the relationship between existence and quiddity turned out to be one of the most important discussions in Islamic philosophy. At the beginning, under the influence of dividing being into necessary and possible types, Muslim philosophers tried to explain the fundamental difference between them through explaining the relationship between quiddity and existence. As a result, they considered two propositions as the basis of two interpretations of existence and the explanation of its relationship with quiddity. The theory of the synthetic nature of quiddative existents in terms of their existence and quiddity, the existence’s being superadded or accidental to quiddity, and the distinction between existence and quiddity in existents are the views that emerged in Islamic philosophy with Farabi and gradually came to the fore as the most important discussions concerning existence. Furthermore, Farabi’s discussion concerning the individuation of quiddities and the criterion for individuation, which was later accepted by all Islamic philosophers and emphasized by them, was developed under the influence of the above theories. In this paper, the writer has initially tried to provide a correct understanding of the theory of distinction through clarifying its fundamental bases. Then he has clarified its ontological and philosophical consequences and highlighted the importance of this theory in Islamic philosophy. Such an explanation necessitates an extensive investigation of Farabi’s ideas about existence, the meaning of existence, and the existence-quiddity relation.

In the history of Islamic Philosophy Ibn Sina and Farabi are known to be originator of the distinction between existence and quiddity. In the philosophy of these two philosophers the distinction of existence and quiddity is used as a proof for the existence of God who is the end of the first philosophy. According to Ibn Sina positively this distinction is based on essential possibility and necessity by something else and this is also is based on a division of existent into necessary and possible being. It is here that the discussion about occurance of existence to quiddity is propounded. Shayh by anticipating what later his predecessors including Ibn Rushed have propounded sometimes has considered this occurrence in view of conception the opposite of essential in the chapter of Isagogue and sometimes has also regarded the connection between existence and quiddity of the kind of relation. But in view of instance (in outside) has considered existence and quiddity as a unified thing.The distinction between existence and quiddity is not propounded in illuminist philosophy in relation to the distinction between necessary and possible being and effective in proving the existence of the Most High. Suhravardi by his own explicit assertion considers the prepatetic philosophers as holding to a distinction between external existence and essence and for this reason has objected to them. But what he has in mind of existence, unlike what prepatetic philosophers have in view, is the concept of existence not the truth of existence.

Avicenna has based his philosophical system on the principle of distinction between existence and quiddity. However, this principle has been criticized by some other philosophers and thinkers in the Islamic world. It has been accepted by many scholars since past times that some of these 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 for Ibn Rushd, yes he did, but, as for Suhrawardi, the answer is no, he did not. Because Ibn Rushd sees Avicenna as a commentator who had misinterpreted Aristotle. While Suhrawardithinks differently. The analysis of Suhrawardi's 'iitibarat aqliyyah' (rational considerations) shows that, understanding the basic differences between Aristotle and Avicenna and basing himself on the new elements of 'anvar-I ilahiyyah' (metaphysical lights]) and 'idhafah ishraqiyyah' (illuminative relation) which are the philosophical explanations of the theorem of 'iijado-shey la min shey' (existentiating the thing not from something), makes him a different critic of Avicenna’s philosophy. Avicenna himself in some cases has mentioned that he has never meant external distinction between existence and quiddity; what he had in mind is a metaphysical and not an external distinction. 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 Avicenna and Ibn Rush pose against external distinction. This may be the reason why some have formed the idea that Suhrawardi misunderstood Avicenna’s distinction between existence and quiddity.

through the various eras of the history of philosophy, Ordinary quiddity has had several meanings and the philosophical terms in Farabi’s philosophy, as a bridge between Aristotle and Avicenna, do not present pose or repute perfectly their aspects and necessities. In spite of its distinction for Farabi Ordinary type quiddity is melded with and close to Existence. The evidence for This claim in Farabi’s writings is where he called quiddity “What the entity is”, “What the entity existence depends on” or “The dole of existence belong to the entity” where quiddity’s parts designate parts of entity existence. According to Farabi the absence of quiddity is the criteria of not existing and possessing an exposal quiddity is the criteria of existing. Therefore for the necessary Existent he affirms Ordinary type unity between his existence and his quiddity instead of his rejecting quiddity. In addition to “What is it?” quiddity is the answer to the questions of “Quality”, “Is it?” and “Due to what”. Moreover Farabi uses “essence”, “nature”, “substance” (correlatively), “thatness”, “definition” and occasionally “reality” in the same way.

In his investigation of the concept of "Being", Aristotle relates the question of "existence" to the question "essence" (ousia) and considers essence as "whatness" and quiddity. Although in his logical discussions he treats the concepts of "existence" and "whatness" separately and makes a distinction between them, but does not extend this distinction to the area of philosophical topics.But in the prepatetic Islamic system of Philosophy, explanation and distinction between "Being" and "quidity" is without doubt one of the most fundamental philosophical doctrines and beliefs. In the history of Islamic philosophy, the theory of metaphysical distinction between being and essence has been attributed to Ibn Sina, but it is Farabi who for the first time has propounded clearly and decisively a two – part division between "being" and "quiddity" and has prepared the way for Avecinian philosophy. In addition to his logical distinction between "existence" and "whatness" of things he has stressed on a metaphysical distinction between them and has made this distinction the foundation of his metaphysical system. From Farabi's view, being is an inherent accident of quiddity.In this article we try to explain the concepts of "existence" and "whatness" of things and their relation as one of the most fundamental topics in prepatetic philosophy in the philosophical thought of these two great prepatetic philosophers, ie Aristotle and Farabi, with specific stress on comparing their views.

The discussion of existence and quiddity and the relationship between them is one of the fundamental debates in philosophy, and various portraits of this relationship can be shown in distinct natural, logical, and philosophical molds. The word “distinct” is a homonym in these cases and has a particular meaning in each one. However, these meanings have been frequently confused with each other in the history of philosophy. One of the innovations of Islamic philosophy is the theory of the distinction of existence from quiddity, which was only possible in the light of understanding the meaning of the truth of existence. Islamic philosophers, particularly Fārābī and Ibn Sīnā, tried to perceive existence differently from Aristotle and not to reduce the question of being to the whatness of objects because of their epistemological distance from the Greek tradition in philosophy. Nevertheless, this approach has also had its own critics. One of the philosophers who criticized the distinction of quiddity from existence is Ibn Rushd. He accused Ibn Sīnā of misunderstanding and heresy regarding the relationship between existence, quiddity, and accidents of existence and believed that Ibn Sīnā had confused the different meanings of existence and the one and had fallen in the trap of sophistry due to homonymy. Ibn Rushd maintained that the origin of the formation of objects is substance and considered existence to be merely a concept that can be abstracted from existing objects. His main criticism of Ibn Sīnā concerning this problem was that viewing existence as an accident for quiddity leads to several misconceptions such as equating existence with substance. However, Ibn Rushd himself had in fact failed to understand the meaning of existence as an accident in Ibn Sīnā’s view. He believed that Ibn Sīnā had equated existence and accident in the sense of a quiddative affair with each other, while Ibn Sīnā’s intention of occurrence of existence to quiddity as an accident was its addition to quiddity.

The issues of Avicenna's philosophy begin with the topicality of being qua being; in the works of Avicenna, the human mind can draw the actualized external existence away into two distinct concepts of existence and whatness. Later this basic question was raised: Which one of the two concepts mentioned in the work of Sheikh is objective and which one is ideational. The following analytical-critical research, while explaining the conceptual principles, is looking for an answer to the question; is the distinction between the existence and the quiddity (whatness) an ontological question or is it merely an epistemological argument? Thus, by analyzing and critiquing recent articles on the field of Avicenna's belief about the question that what is the reality: the primacy of existence or primacy of quiddity is concluded that this argument -the question of the primacy of existence or quiddity- has no place here; Because these two have an identity with each other in the objective world; So with no external changes, talking about the fundamentality of existence and ontological fundamentality of quiddity is merely an epistemological problem. So in Avicenna's work, actualized external existent is a reality and in that sense it is authentic; so, it is separated into existence and quiddity in the mind of the perceiver.

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In addition to a study of the major interpretations of the "principality of existence", (ʾIṣāla al-wujūd) this article studies Mullā Ṣadrā's view through the third person narration method. According to this method, the main point in "principality of existence" is the distinction, the rules and the relation of existence and quiddity. Mullā Ṣadrā describes his view in the form of the proposition, "Existence exists", and he claims that this proposition is a "common technical Predication." This proposition can be interpreted as follows: 1. Quiddity has instantiations in the external world. 2. Quiddity does not have any instantiation in the external world. 3. Quiddity, primarily, does not have any instantiation in the external world, but it has instantiations through existence. There are many explanations for each of the three interpretations. The major point of this article is that it is not possible for quiddity in-itself to exist in the external world.

This paper considers the Allāma Ṭabāṭabāī’s Ṣiddīqin argument from a new point of view. First، his particular philosophical foundations of the argument are clearly expressed and after that، four different versions of the Ṣiddīqin argument are presented. In one version، we have concerned with the explanation of the argument on the basis of the broad sense of reality، while in another version، we have presented the argument as a sound one which is based on denial of metaphysical distinction between quiddity and existence in reality as well as the notions of absolute and conditioned reality in Ṭabāṭabāī’s view. Furthermore، we have examined other versions of this argument. As a result of this inquiry، those versions which are based on the broad sense of reality and particularly on denial of metaphysical distinction between quiddity and existence in reality، because of focusing on particular philosophical foundations of Allāma Ṭabāṭabāī، are sound and successful، while other versions are insufficient both in interpreting Allāma Ṭabāṭabāī’s view or in representing an argument for the existence of God.