I’ve been reading a bit of Scholastic and Islamic Golden Age philosophy – namely Thomas Aquinas and Abu Ali al-Husayn ibn Sina (Avicenna). In those times, people were obsessed with two things: the Greek philosophers (Plato, the neoplatonists, and Aristotle) and being able to reconcile the Grecian ontology with their monotheistic, Abrahamic religion. It’s interesting to read their philosophy, but I was wondering if it had any relevance to modern philosophy.

Both Aquinas and Avicenna took Aristotle’s idea of separating existence from essence and substance from accidents and tried to reconfigure into their own ontology. Existence and essence, in Aquinas’s ontology, combine to make Being. Being is what is; essence is the what and existence is the is. Existence, in both Aquinas’s and Avicenna’s terminology, means actuality – that a thing is. Essence is what makes that thing into that particular thing. Essence is potentiality while existence gives essence actuality.

Avicenna hinted at the idea of God bestowing actuality (existence) onto essence during creation, using emanationism. In Avicenna’s system, God is a necessary-in-itself existence that acts as the first cause that creates the rest of the universe, which was only potentiality as contingent existence. Once existence was bestowed upon this potentiality (essence) it became necessary-due-to-other (due to God, the necessary-in-itself) existence.

Aquinas was more explicit that it is God who ‘bestows’ existence onto essence in order to make it actuality. That is how Aquinas believed God created the universe. In this, God is necessary in an Avicennan sense in that God is the only Being whose existence is implied by His essence. Because God is existence by essence, He is the efficient cause of the universe, which makes the efficient cause antecedent to the material and formal cause of the universe, because it was God as efficient cause that created matter and form from nothing.

Of course, in the twentieth century, Jean-Paul Sarte famously said that existence precedes essence, which is the reverse order of what the Medieval philosophers thought. In this line of thinking, a thing first exists, and then due to its form of existing, it has essence bestowed upon it by observers. This is where the Existentialist idea of radical freedom came from. In the Medieval philosophy, you were your essence first, and it was God that bestowed upon you existence. But that means your essence is immutable. In Existentialism, it is you that creates your essence to be what you want, and your essence is only determined by what you do, not by your intentions.

What I wonder, though, is if this idea of separating existence and essence can work in a quantum mechanical sense. What is existence and essence in the subatomic building blocks of our universe? Is the essence of the electron its negative charge, it’s mass, it’s waveform, and all of those things? Or are those just contingent accidents? Ontologically speaking, what gives leptons, quarks, and bosons existence? Is existence a part of their essence in the way Aquinas conceived of God – by their very nature, are these elementary particles necessary-in-themselves? Is there existence inevitable due to their very essence? Or is the essence-existence divide something only we humans use as a way of understanding the universe?