The world around us is populated by distinct, natural kinds of things.
It's a simple but significant truth.
Over the course of our lives, we encounter a variety of different things.
It's just common-sensical.
There are human beings, kangaroos, cactuses, stars, et cetera.
What is more, this diversity of kinds is irreducible.
We can't reduce it all down to some one unique thing.
Some of the pre-Socratic philosophers tried to explain everything as elemental fire or
water, as if there were only one element underneath everything.
Many contemporary scientists try to explain everything as ordered bundles of chemicals,
molecules, and atoms.
One problem with this is that it cuts against the grain of common sense.
The ordinary living beings we see around us are wholistic and unified and don't seem
reducible to mere bundles of atoms.
Another problem is that these material building blocks themselves are diverse.
There just are distinct atomic particles and chemical elements.
How do we account for this complexity?
The attempt to reduce everything to only one kind of thing is ill-fated, and it doesn't
work.
Let's call every natural kind, like a human being or an oak tree, a kind of essence.
Each essence has material parts, but is also a wholistic form.
The material parts are organized and made intelligible by the form.
What do I mean by this?
Take the material organs of a human being, like the heart, lungs, liver, and brain.
These organs all function as the organs of a whole animal, as dynamic parts of a living
being.
The kind of thing that the human being is gives order to all these parts, and they have
their function in view of the purposes or functions of the whole human being.
So for example, we breathe oxygen, or we have sensations, we digest food, and so forth,
in view of a host of more important human activities, like reasoning, friendship, family
life, prayer.
The organs all participate in the natural form, in this case being human, which exerts
influence from the top down as an organizing principle from within.
We see this at the lower levels within ourselves, as well.
So for example, in organs.
The gallbladder consists of various cells, but the cells are organized by the gallbladder's
nature and function.
We can predict their behavior based on the fact that they are cells of this particular
kind of organ.
The larger point is that in all the things we experience, there's both form and matter.
Reality is not simply built up from the bottom.
It's also influenced from the top down.
The parts of things have their place within the whole.
This is what we denote when we speak of material essences.
The essence gets at what the thing is as a form-matter composite.
When we think about what a thing is essentially, we think about its distinctive nature, or
formal features, and about its typical material constitution.
So we think about both form and matter.
And once we have established the notion of essences, we can begin to account for how
things differ.
The nature of the kangaroo is different from the nature of the human being, or the star.
The nature of the gallbladder is different from the nature of the heart, or the liver.
The parts of things are arranged differently because they are parts of different things
for different ends.
The human heart is quite different from the stem of a plant.
It is the nature of a given thing that gives shape and definition to the material parts.
Now, once we've acknowledged that there really are distinct kinds of things, different essences
you might say, in the world around us, we could also begin to think about the presence
of something common within all of them, something common to stars, and human beings, and kangaroos.
They're all united by the fact that they all exist.
They all have being.
A good summary statement is that essence answers to what a thing is, while existence, or being,
answers to that it is, or the fact that it exists.
Notice that this means that all these diverse kinds of things all exist.
Existence is something common to all the various kinds of things that are, no matter how different
they are.
This shows us that the philosophical mystery of our nature, our essence, is distinct from
the mystery of our existence.
They're related topics, but they're also distinct.
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