Aristoteles De Anima (Nefs Üzerine) adlı eserinde nefsi bitkisel, hayvani ve insani olarak üç türe ayırır. Bu tasnif aynıyla İslam dünyasına aktarılmış ve orada da bu tasnife sadık kalınmıştır. Bununla birlikte nefse dair ortaya konulan teoriler Aristoteles’in teorisinden oldukça farklılaşmıştır. Bu teori, İslam Felsefesi içerisinde sadece zenginleştirilmekle kalmayıp hem felsefe ve kelam hem de tasavvufi düşüncede bilgi, nübüvvet ve ahiret gibi konuların işlenmesinde vaz geçilmez bir müracaat noktası haline gelmiştir. İbn Sînâ, nefis konusuna kendinden önceki Müslüman Meşşâîlerden çok daha fazla bir önem verdi. O, nefislerin ilk var olduklarında bireysel bir mahiyete sahip olduklarını kabul etmemiş; aksine nefislerin ilk aşamada bitkisel, hayvani veya insani olmak üzere türsel bir mahiyete sahip olduklarını benimsemiştir. Ancak bu durumda nefislerin bireysel kimliklerini nasıl kazandıkları bir sorun olarak karşımıza çıkmaktadır. Bu çalışmada nefislerin bireysel kimliklerini nasıl kazandıkları sorusunu hem İbn Sînâ’nın hem de ondan ciddi ölçüde farklılaşan Ebü’l-Berekât el-Bağdâdî’nin görüşleri doğrultusunda inceleyeme çalıştım. İbn Sînâ’nın nefislerin türsel mahiyet bakımından ortaklığını kabul ederken Ebü’l-Berekât’ın bunu reddetmesinin neden ve sonuçları üzerinde durdum. Ayrıca her iki filozofun teorisinde nefislerin bireyselleşmesine etki eden faktörlerin neler olduğu burada üzerinde durulan diğer bir konu oldu.

Aristotle’s de Anima had a significant influence on those who wrote about the soul after him. The traces of the influence can be followed easily in Islamic Philosophy as well. In this work, he defines the soul as a first actuality (entelecheia) of a natural body that has life potentially and he divides it into three types as a nutritive, sensible, and rational soul. This classification was inherited by Muslim philosophers and remained there as it was. But, with this obvious effect, the theories presented about the soul in Islamic Philosophy were considerably differentiated from Aristotle’s. This theory was not only enriched within Islamic philosophy but also it differentiated from the Aristotelian line about subjects like the relationship of body soul and maintenance of its personal existence after the separation from the body. On the other hand, the theory became an indispensable reference point in the fields of  Islamic Philosophy, Kalam and Sufism about the examination of some issues such as knowledge, prophecy, ethics and the afterlife. Ibn Sīnā gave much more importance to the soul theory than other Muslim Peripatetics. He did not admit that the soul exists with its individual essence before coming to the body, on the contrary, it individualizes through the body. Also, he acknowledged that the soul in the first step has only species essence as vegetative, animal and human. In this case, however, how the souls have had their individual character arises as a problem. In this work, I tried to examine the question of ‘How the soul acquires its individual characters’ in the thought of Ibn Sīnā and Abū al-Barakāt al-Baghdādī who severely differentiated from him. And, I tried to determine the factors that have a decisive role in this process. I also dealt with that while Ibn Sīnā accepted typical essence of the souls and why Abū al-Barakāt rejected this and adopted their individual differences. Both Ibn Sīnā and Abū al-Barakāt reject the existence of souls before the body’s existence, and they accepted that their existence is simultaneous. Their arguments on this subject are mainly based on the explanation of the differences between human characters. However, Abū al-Barakāt develops a different argument based on the fact that humans reach knowledge after their ignorance.Muslim Peripatetics refer to the Agent Intellect as the existence which gives souls. But Abū al-Barakāt does not give a place to the Agent Intellect in his philosophy and rather he directly refers to God as the giver of souls.Ibn Sīnā’s thought regarding wherefrom souls attained their existence is not clear. His opinion about the subject can be understood as species souls are created on the sky by the Agent Intellect and then they are sent to the bodies. However, this interpretation will lead us to the conclusion that is not acceptable for Ibn Sīnā; since this requires that souls have their existence before joining the body. In that case, it is appropriate to understand Ibn Sīnā’s words that ‘Agent Intellect sends souls to the body’ as it creates appropriate souls in the bodies. On the other hand, the view of Abū al-Barakāt on this topic is that the souls are created in the bodies directly by God.Ibn Sīnā accepts that souls exist in a species essence. Since he points out that souls have common features that enough to be called as a species. Besides this, the idea of an Active Intellect has an effect on this theory.According to Ibn Sīnā species souls acquire their individualities after joining the bodies as a result of some factors that are effective during he soul’s existence process as well as factors (such as mizāj) that arise from the bodies. In spite of that, Abū al-Barakāt accepts that all souls come to existence with their individual essence rather than species essence. His view relies upon that every soul has consciousness of their individual differences. Everyone is aware of that his/her soul is belonging only to him/her and he/she is not sharing it with others; so each soul is not species essence. According to him, every owner of the soul has this consciousness at a different level, even if not at the self-conscious level. One of the reasons behind his argument is his rejection of the Agent Intellect.Some other factors can be traced behind the claim of Peripatetics that every soul that conjoins the body is not different in terms of their individual essence. At this point, we can do some evaluations based on their acceptance of the soul as the main principle of movement. Both Aristotle and Ibn Sīnā use the argument that sets out from the movement in an animal for justification of the soul’s existence. In this situation, the soul becomes a source of movement in all animals and this transforms the soul into a being whose main function is movement. If so, even though beings differentiate from each other, the reason that determines differences will not be the souls but rather souls will just be a factor that gives the same effect in different animals and souls will be a member of the same species. Even, in this case, Peripatetic philosophers – such as Ibn Sīnā- divide the soul into three types as nutritive, sensible, and rational, in fact, it would be more compatible to say that this classification is not essential. As a matter of fact, the first function of the soul is movement. The fact that the change in the form of the movement (some existences have only growth movement, some have spatial displacement movement and others have voluntary movement) does not originate from essential differences of souls but it arises from the instruments of bodies where to souls join. Thereby, saying that these species differences of souls are not resultant from the souls’ nature will be more compatible with this Peripatetic theory. In fact, when we consider that Muslim Peripatetics accept the Agent Intellect as a unique agent of all souls and they remain loyal in their thought to the principle “from one thing only one thing could proceed” then it will be more reasonable that souls are the same in terms of their essence and the differences between them occur because of some factors after they conjoin to the body; so that these differences are accidental, not essential. In that case, we can understand why great Peripatetic philosopher Ibn Rushd talked about the soul without dividing it into three types. He only refers to different powers of the soul without acknowledging the triple division of the soul that is famously from the Peripatetic philosophers. As for Abū al-Barakāt, aside from confirming the soul as a principle of movement, he also highlights it as a source of self-consciousness, he argued that not only at the species level but also at the individual level each soul differentia from each other. And his emphasis on the individual differences of the soul resulted in rejecting the Agent intellect or at least could not find a functional place for it in his theory. At that point, we can say that the essential difference between Abū al-Barakāt and Muslim Peripatetics like Ibn Sīnā is that his stressing on the relation between the soul and self-conscious.Another consequence of the claim that souls are common to a species is related to the quality of the sense of self-consciousness. When it is claimed that souls are common with the species essence then it cannot be argued that the soul has self-consciousness essentially. In this case, it is necessary to accept that self-consciousness is a result of different factors that include the body. This degrades the self-consciousness to an accidental position. When it is acknowledged as Abū al-Barakāt defends that each soul has individual differences, then the self-consciousness will be an essential sense of the soul and the soul has it since its existence.