Aristotle (384 BC ? March 7, 322 BC) was an ancient Greek philosopher and a student of Plato, considered first scientist in Western world. He was a philosopher of common sense. He tried to define essences and his aim is to explicate the world as well as cosmos surrounding us. According to Introduction of Metaphysics, Aristotle's world-view is teleological that there is kind of purpose in cosmos: " What is important is that the world seems to have a purpose, a meaning and even a design. It is an ordered structure, a cosmos, and it may even manifest the invention of a Creator." (p. xvii)
The Metaphysics is Aristotle's significant philosophical work, that contains the theory of being. The word "metaphysics" is defined due to the fact that this work was positioned right after "physics". On the other hand, it is accepted because the purpose of metaphysics, which is to reach beyond nature (physis), and to discover the ultimate essence and the reason for being. Moreover, one of the central themes of Aristotle's philosophy and metaphysics is theory of Potentiality and Actuality, which is considered in regard to being and change in Book Theta.
First of all, Aristotle defines substance (ousia) as ultimate and an underlying reality, or as the fundemental element of all existing things. Substance is the reality of individual things, and what is not substance is properties, also accident (not neccessary). The substance of each individual thing, the particular nature of that thing, is that which does not belong to other individual things, whereas the universal principle or element of an individual thing is that w ...