Essence and Existence in Aquinas's Ontology

One of the greatest Theologian that ever lived perhaps was Aquinas. His classical arguments for the existence of God was being used in apologetics and analyzed by scholars hitherto. Beside that, his other view on the distinction between essence and existence is worth to be studied and capture our attention. The importance of this subject best described by Antony Kenny an expert of Medieval Philosophy says, "the theory of the real distinction between essence and existence, and the thesis that God is self-subsistent being, are often presented as the most profound and original contributions made by Aquinas to philosophy."

Basically, being constitutes of two elements. First, existence. Second, essence. Two elements are necessary in order something to be. Why bother with these two words which sound so airy fairy and remote? Part of the answer is that in language discourses, many words has not been investigated deep enough yet and thus, analyzing the word from certain philosopher will help us to fill the gap of the of our current knowledge of some particular words, and gain better understanding to be able to engage with certain philosophical concept better. Moreover, to reason and study the Medieval metaphysics or Metaphysics in a very broad sense, one need to know at least the meaning and significance of the world essence and existence. In fact. These two ideas are repeatedly will be mentioned again and again, especially by Aquinas or Aristotle. "If human by nature desire to know", said Aristotle, it is good to be able to know the meaning of those words better and be able to know the differences between them.

In Aquinas's ontolology, Essence is the "whatness" of thing (What is). For Aquinas, essence includes form (Aquinas differentiate between substantial Form/Forma Patris and nature of Essence/Formae Totius) and also matter as the substance of being. It is the principal materials that make something into a same kind/category/nature of being. What makes man as man, what makes tree as tree or horse as horse. The essence encompasssed the diffrentia and also specific genus, that's what he mean by essence (Essentia qua res denominatur ens-Essence is that by which a thing is dominated a being). Let us take the concerete example of essence. To be human in nature/essence is to have body and soul. Although both can be distingushable, both cannot be seperated. If there is a seperation between body and soul, this is the sign of death occurs. Aquinas promote duality rather than dialism. In relation to knowledge and essence, every mode of knowing is basically is to know of one essence/nature. To be known also means to be known by its nature/essence. 

Existence is the act of being (esse), which supperior to essence. Supperior here is in the sense of existence prior to essence and "the most formal of all."Esse is what makes the potential essence actual and it is grounded in God as the Pure Act, and as the prime mover, in Thomas Aquinas Metaphysical framework (causal causes/agent). To put it more plain existence is the thatness of thing. Accoding to Anthony Kenny in his works Aquinas on Being, there are actually several categories of existence that Aquinas made, kenny categorized it into tweleve. First, specific existense is not predicate, it is like X of something for instance extra-terrestrial being. Second, Individual existence.This existence belongs to predicate, to human being. Third, Substantial being. This existence refer to the stetement/status of indiviual existence for instance he is gone/passed away (S is P). Next is accidental being, accidental being is what inheres or characteristics of an individual existence. For instance Socrates is wise. Fifth, is Common being, it refers things and animal in the universe. Futhermore is actual and also potential being. Actual being us simply an after product of pontentiality for instance butterfly as oppose to catterpillar which is the potential base. Futhermore is absolute being, which can refer to God as the ultimate source (The only pure act according to Aquinas). The next is intentonal being, is the X that comes in mind when we think of particular X. Next is fictional being, is a being that treated to be a real being.  Possible being is the idea of X that yet to be realized. For instance before Caesar there were already Julius Caesar like characteristics (ideal prototype), lacking only his real existence. Next is predicational being. Is the language "to be" that used to join the predicate. Lastly is identical being. Is refer to identity, for instance A is B and the reverse is also true that B is A. 

Apparently, Aquinas borrowed heavily the language of essence and existence from Aristotle to articulate his theology. Some writer even says that he is quite eucemenical philosopher, which borrows lot of term and thoughts of philosophers in his works and writing (Neo-Platonic, Boethius and Avicenna influce also can be seen in his works). This can make ordinary people doubt whether he was promoting theology or philosophy however, both should never be problemetized. In those days Theologian is philosopher and most philosopher were theologians as well. Undoubtedly, his concept of essence and existence could help us understand the nature of things and God with a deeper and more precise language.