On the Distinction between Essence and Existence

Although Aristotle takes matter more seriously than Plato does, it can be argued that St. Thomas Aquinas takes matter much more seriously than does Aristotle. For Aristotle, essence is, as it was for Plato, the form. But this is not so for Aquinas. If the essence was simply the substantial form, then matter is outside the essence of a thing. But am I not essentially a material kind of being? For Thomas, the essence of a material thing includes matter and form. A human being, an animal, a rock, are essentially material things.

But what accounts for the fact that a person is "human"? The answer is the substantial form, that is, the soul. What accounts for the fact that a human person can die? The answer is his matter. Form exists in matter, and matter is the principle of a thing's potentiality. What accounts for a thing's extension? The accident 'quantity'. What accounts for one's ability to laugh? One's power of intelligence.

But what accounts for the very fact that a thing exists? There is nothing in the substance itself that requires it to be. Prime matter is the material cause, rendering a thing perishable, the substantial form determines the matter to be a certain kind of thing, ie, rabbit, or gold. Quantity gives the rabbit or the gold parts outside of parts. Quality is the accidental form that qualifies the gold in a particular way, etc.,. But there is a distinction between what a thing is, and the very act of its existence. One can study "what something is" without knowing "whether or not it actually exists". We can study certain frogs, that is, we can come to understand "what they are", but that very knowledge does not enable us to determine whether or not those frogs actually exist. For St. Thomas, there is a real distinction between essence, which answers to the question "what is it?", and existence, which answers to the question "is it?". This is a departure from both Plato and Aristotle, for whom ousia meant essence or being.

For Aquinas, a being is a habens esse: that which has an act of existing. In other words, a being is not simply substance. A being is a thing that has an act of existing. This means that for St. Thomas, the whole substance is in potency to existence. It does not have existence by nature. You and I have a received existence. Consider that it is correct to say: you are human (you are your essence). But it is not correct to say: you are existence (you are not your existence). Rather, one correctly says: you have existence. An existing being exists not by virtue of its substantial form, but by virtue of its esse, that is, its received act of existing. The substantial form is the act of matter, but the esse of a being is the act of being. The act of being is the act of the substantial form, as well as the act of the accidents. Without esse (the act of being), there is no being to speak of.

The above diagram is merely a visual representation of a being whose essence is distinct from its existence, such as a human, or a dog, a carbon atom, etc. Now, recall that the definition of a thing expresses a thing's essence. Whatever belongs to a thing's essence belongs to it necessarily. A triangle is a three sided figure. Hence, a triangle is necessarily three sided. Man is a rational animal. Hence, all men, no matter who they are, are necessarily rational creatures.

Whatever does not belong to the essence will not be included within the definition of the thing, and therefore will not belong to the thing necessarily, but contingently or possibly. Notice that metal, yellow, large, etc., is not included in the definition of triangle, even though some triangles are metal, yellow, and rather large. This means that a triangle is not necessarily metal, yellow, and large, but possibly. So too, blond hair and blue eyes do not belong to the essence of man, otherwise all men would have blond hair and blue eyes, and anyone who does not is not a man. Hence, it is necessary that Mike be rational, sentient, that he have a will, that he have the potentiality to walk, the power to see, remember, etc., but it is not necessary that he be tall, blond, German, etc. Moreoever, if the power to walk, see, or hear, etc., cannot be realized in a human person, it is not due to the person's nature, but to some deformation rooted in poorly disposed matter, ie eye damage, oxygen deprivation to the brain, no legs due to an accident, etc.,.

And so whatever belongs within the blue area in the above diagram, belongs to the thing necessarily. Anything outside the essence belongs to it possibly or contingently.

But if existence were part of the "what" of Mike, that is, part of his essence (within the blue area), then Mike would necessarily exist (since whatever belongs to the essence of a thing belongs to it necessarily). In other words, it would be essential for Mike to exist. And just as a triangle cannot not have three sides, and a human being cannot not have the power to reason, and a bird cannot not have wings, Mike could not not exist. He would have always existed, exists now, and ever shall be. But we know this not to be the case. The act of existing is received. Mike came into existence. He is not existence, rather he is human. The act of existing is had.

Some Points on Epistemology

Aquinas agrees with Aristotle that "nothing is in the intellect that is not first in the senses." But the passive intellect does not just become a form. The passive intellect receives the essence of the thing known. The essence receives a new kind of existence in the intellect. Outside of the mind, the essence is particular, in the here and now. That tree has existence outside of the mind. It is there, now, actually green and brown, actually large, etc.,. And it is particular. But essence and existence are really distinct. The active intellect abstracts the essence from its individuating conditions, and after impressing the essence onto the passive mind, the essence acquires a new kind of existence (an intentional existence, or a logical existence). The essence exists universally in the mind. The tree has not changed. The tree is still there, a composite of essence and existence. But the essence is existentially neutral (it can exist in the mind or outside the mind). It need not necessarily exist in any particular way. The intellect, in knowing things, gives the essence a new existence (an intentional existence). The essence is capable of existing universally, because the essence is a potency to existence. It receives a different kind of existence in the mind, an immaterial existence, a universal mode of existence, an abstract mode of existence, unlike its existence outside of the mind.

The Acts of the Intellect

The intellect apprehends, judges, and reasons. But there is a difference between them. The first act of the intellect is called simple apprehension. This act is the apprehension of the thing's essence. Now the intellect apprehends essences, but essence is not existence. I can know what a thing is, but that knowledge is not a knowledge of whether it is or not. So, how does one apprehend existence? By a distinct act of the intellect. This is called existential judgement. This marks the second act of the intellect. And the third act of the intellect is called reasoning. When we reason deductively, for example, we draw a conclusion from two prior premises: All men are mortal, John is a man. Therefore, John is mortal.

I know what a thing is (essence) through simple apprehension. At the same time, I know that it is (existence) through judgement. The two activities occur simultaneously.

Next Page: Chapter 19: The Existence of God
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