Based on insightful study on the theory of "first principle" and Plato's theory of "Forms ", Aristotle has proposed the theory of OUSIA and used it as basis of his ontology. However, this theory has been subject to some precise criticisms.Discussing the formation process of this theory, the present paper elaborates on some of its conceptological problems based on Aristotle sayings. "Nonprediction on subject" and "non-existence in subject", as two main features of OUSIA, is a kind of attribution to generals and accepting contraries while holding numerical unity of OUSIA is not acceptable, because it is subordinate to differentiation between psychic and relative features of object and Aristotle has not elaborated on this differentiation.

Avicenna may be regarded as the first Muslim philosopher who has perceived a deep connection between Aristotelian concept of OUSIA and being and, analyzing the concept ontologically, he tried to correct the failures of Aristotle’s thought in this field. In this way, the ambiguity of the subject-matter of first philosophy has been omitted and the capability of Aristotle’s philosophical teachings is used for establishing a religious philosophy. As is explained, in spite of considerable changes made in contemporary studies on Aristotle`s philosophy, Avicenna can be regarded as a perfect authority in this field.

Aristotle’ s discussion of the OUSIA are diverse and confusing since there are various definition of the term especially in Metaphysics, Physics and Categories. He refers to it sometimes as the underlying layer, sometimes he means something similar to the meaning of being, and sometimes as essence and quiddity. Hence, the difficulty and disagreement among the translators and interpreters on the best equivalent for OUSIA in other languages. In the present paper, after a short historical discussion about OUSIA, I examine some common equivalents for the OUSIA in Latin and English and attempt to discuss the different reasons for and against each equivalent. My argument, in general, goes for the term Substance, and I will bring 8 reasons to establish the argument.

The word “OUSIA”, derived from “eimi” (“to be”) is only of the most fundamental concepts in Aristotelian ontology. In spite of its importance, however, Aristotle’s texts regarding this concept and not uniform and, in addition, the equivalents which most translators have selected or coined are open to criticism. The first Latin translators chose essentia, which was a faithful translation in so far as it signifies ‘being’, however it was not long before this translation was replaced with substantia, which is a bad choice. The English form of the wrong choice, i.e. substance, was also accepted by most English translators and still prevails. However English speaking experts have taken to revising this translation and the word ‘entity’ has gradually gained acceptance. In Arabic speaking domains this problem remains and no measures of redress have been taken. None of the possible words, such as dhat, jawhar and tabiah can perform the function of οusi. Needless to say, such a state of affairs has left a negative impact on the understanding of Aristotle’s ontology.

Aristotle's view on the structure of being is based upon OUSIA, first matter, form, potentiality, actuality and entelecha. In spite of his detailed studies for introducing OUSIA, as the most fundamental problem in first philosophy, the concept has failed to be well introduced and remained ambiguous. Aristotle is not certain when introducing the cases of OUSIA. In some cases, he has known form, and in others the thing compounded of form, matter and accidentals as real OUSIA. Nevertheless, he has known matter as the cause for singularity and determination of natural beings. All three beliefs has been criticized. Aristotle, however, relying on such weak concepts, has been led to an unmoved OUSIA and described it as pure entelechia. This view is not correctly based either. In the paper some failures of his thought have been described.

Criticizing Plato’s theory Aristotle brought down the ideas from heaven to earth and explained ideas as an internal content of particular things and then called it primary being or substance which is identical with essence. Then he logically defined OUSIA so that depicted the logical structure of world. But his critique of Plato forced him to explain the theory of form and matter as two fundamental substances which need each other. Thereby he was forced to develop a theory that would indicate OUSIA as being abstracted from the particular things. Naturally Aristotle was made to deal with some problems and questions. So he attempted to solve these problems through active and passive reason. However, this article shows that Aristotle’s theory is not provable anymore. Against this theory, Husserl spoke of subjective flow correlates with objects ordered systematically. Here, after explaining Husserl’s view on noema and noesis we come to the conclusion that form and matter are not divided as two separate substances, but they are provided by reflection over intuition and expressed by language. In the end it would be cleared that abstraction is explainable only through phenomenology and thereby we can explain that all scientific and reasonable systems are founded on living world.

The present article is an analysis based upon Treatise of Z. The purpose of this article is to present the form found in Treatise of Z in Aristotle’s Metaphysics. This form is OUSIA-substance. It is the principle of determinacy and intelligibility for individuals. This form is associated with matter. Form of this type, the principle for material individuals, may be called substantial form, although Aristotle dose not use the term. Substantial form is neither a universal nor an individual. Form in Aristotle’s view is different from an "Idea" in Plato’s. The distinction is not that the one is associated with matter, while the other is not. Aristotle uses the expression "this" of form and of individual thing. A universal is not a "This" but a "Such".

Aristotle, in all his works including Metaphysics, Physics and Generation and Corruption, wherever expressing a view on an issue, makes references to Plato and other philosophers who preceded him trying to present flaws in their thoughts. To begin with critique is Aristotle’s specific philosophic method. Especially in Metaphysics, which, inhis words, is the knowledge of ‘being in itself’ dealing with the what and why in all beings, he had to first consider and criticize the well-known views of his time among them the most vexatious one was that of Plato. Aristotle’s fight with Plato’s ‘theory of ideas’ started from the time he was a student of academy. His brief thesis ‘on ideas’, peri ideon, belongs to that era. The present article classifies Aristotle’s objections to Plato’s ideas trying to show their essence and intensity. To this end, the author’s have adopted a neutral stance toward the issues in their analysis and classification of the objections.

Aristotle’s theology is founded upon his physical studies. Aristotle, originally following the goal of pre-Socratic natural philosophers, has organized a set of philosophical concepts including OUSIA, matter, form, potentiality, actuality and entelechia to explain natural changes and motions. His way of study, therefore, is based on experience and observation. In this way, he has proved the existence of an unmoved mover and presented a concept of God. Yet, the failures and ambiguities of the concepts, their essential state of naturality and Aristotle`s main mental concern in solving the problem of nature have led to an ambiguous and defective view in the field.

According to some interpretations, Aristotle's metaphysics is not a coherent and unified work and does not follow a single issue; in other words, in each two or three books a subject is introduced as a subject of metaphysics.; For example, in the fourth book, Aristotle refers to a new phrase “ being qua being” and in the seventh book, he used the term “ OUSIA” as the subject of this episteme. In this paper, we try to clarify Aristotle's view of these terms, as well as their relationship with each other, and also with other concepts that play an essential role in Aristotle's metaphysics (such as the concept of essence and form). In this way, it becomes clear whether an alternative interpretation can be presented to show that Aristotle has been able to establish a new episteme with a new and unique subject in this book and has been able to respond to the difficulties of the Beta book (aporia of Beta) as a the guideline of Metaphysics. By concentrating on four books of Metaphysics (I, III, IV, and VII), this article tries to investigate the above items and show Aristotle's innovations in some positions, as well as some aspects of his philosophical differentiation of Plato's philosophy.