I insist that at this point you read a book of Thomistic metaphysics; I unfortunately only have so much time on my hands. But I do not want to abandon this thread, so I will again offer brief comments.
I am having some hard time wrapping my mind around such notions as essence (quiddity) and existence (esse). As an aside, however, I read that there exists a difference between a concept and a notion. Do you think you could explain it?
In what context was this stated? I could speculate about the difference, but I have no way of knowing how the writer intended to distinguish the two.
But I am having a hard time comprehending why the distinction between a thing’s “whatness” and its "esse is actually real.
How exactly this is spelled out depends on the ontology you use, because in order to describe the difference you need to be able to say something about the act of being (
actus essendi) itself. In Thomistic metaphysics, God is beyond being inasmuch as His essence is existence. Everything else, all substances, have some act of being “limited” by an essence. The essence does not contain anything to account for its own existence; this is why there is a real distinction.
You may have a hard time understanding this because it’s neither obvious nor demonstrable. Many philosophers disagree with it, and it uses an ontology which presupposes Christian theology (especially the so-called metaphysics of Exodus).
Do you think you could differentiate for me, what is the difference between a human being’s essence and his existence?
I believe someone answered this. Again, this way of speaking presupposes an ontology, and especially an act/potency distinction. A human soul, which is the substantial form of the human body, is “act” if we consider prime matter to be “potency”, and “form” if we consider prime matter to be “matter”. But a soul is neither “act” nor “form”
as such. Instead, the soul is the vital principle (or mode of existence) of a human being, whereas the matter is the spatiotemporal principle (or mode of existence); united in a single act of being, they make a human being. Moreover, dimensive matter (in the form of sperm and egg) pre-exists the soul, and so is itself a separate substance which undergoes a substantial change upon ensoulment. Once the soul is created (probably upon conception), the form-matter composite is a human being. However, the soul itself can exist independently of the body, which means that the soul is also an essence joined to an act of existence.
And what about the souls of the dead? Are they essences, beings, or substances? The way I see it, to be dead is to still possess essence and existence, and thus, being but could it not be said that their essences and their substances are incomplete, since they are no longer united to their being. Is this a satisfactory hypothesis?
Yes, a human soul is not a human substance; it is incomplete. I believe someone answered this.
I would like to know, does St Thomas posit a real distinction between “essence” and “esse” because it is possible for things not to exist or to be as actual substances? As I understand it, essences are first those concepts that exist in the Mind of God. Is it correct more exact to say that they exist in the Mind of God, or should it be said that they exist before the Mind of God?
Essences have some reality prior to their existence, but by “reality” is meant that, in whatever way God can be said to possess reason, He knows and can create these essences by limiting an act of being by them.
Can essences be related to Plato’s Theory of the Forms or of the Ideas? The notion that beyond the world of sensation, exists a world of abstract and ideal forms which are more real than the material world?
Yes, the idea of some ground of being limited by forms is certainly influenced by neo-Platonism.
Is this what reality is, that which is present before the Mind of God?
I suppose I’d say that reality is whatever God sustains in being.
So, substances are things that which exist in and by themselves are not said to exist in another. Accidents are those things that exist in another, and are said of another. I understand that a substance, in reality, is a natural kind of thing that exists in its own right. But concretely speaking, what does that mean? According to Aristotle there are 10 categories which are substance and its 9 accidents:
Quantity, quality, relation, action, passion, time, place, disposition (the arrangement of parts), rainment (whether a thing is dressed or armed, etc.).
As far as I can comprehend, all these characteristics fall under and are perceived by the senses. But if you take away all those 9 categories, what is left is a substance. In this case, then, what is substance? Can a substance in itself, even be perceived by the senses?
Accidents are real beings but they are not substances. For example, someone who fathers a son is then and forever in a real relation of fatherhood to the son. Another example: if Socrates is white then he really has whiteness, but we can remove whiteness and still have Socrates. Is this not clear from Aristotle? A substance is a category of being. Only God transcends all categories of being.
Neglected to say: There is no such thing as a “bare” substance. The object of the human intellect is always an essence or quiddity joined to an act of existence. Whether you perceive substances or accidents (which depend upon the existing substance in which they inhere), that is what you are perceiving.
but I will offer the little I know anyways. The doctrine of Divine Simplicity is probably at the heart of the solution to your question here.