All other entities are either said of them as subjects,
those are the universal substances.
Or, in them as subjects, those are the particular inherent items.
Or, have as their subjects items that do one of these two things.
Those are the universal inherent items, and note,
there are no arrows of dependence leading away from particular substances.
These have no subjects, but they are the subjects for everything else.
That makes them the most fundamental kind of being.
They underly everything, with nothing more fundamental that underlies them.
That is why Aristotle calls them primary substances.
He concludes in chapter five.
What is called substance most fully, primarily, and most of all,
is what is neither said of any subject nor in any subject.
For instance, an individual man or horse.
And all other things are either said of the primary
substances as subjects or in them as subjects.
As subjects for all other things,
primary substances are the most important or fundamental kind of being.
In fact, that's pretty much what the word translated substance means.
In Greek, it is ousia,
which is an abstract noun formed from the participle of the verb to be.
A more literal translation would be being-ness, and
a perfectly good rendering would be reality, where reality stands for
genuine or first class as opposed to derivative,
parasitic, or second grade being.
To call something an ousia is to confer a special,
high-grade ontological status on it.
Something that is lost in the translation substance since as we use the term,
we tend to think of substances as things you can spread, handle,
spray out of a can, or get stuck in your hair.
It's not an honorific term in the way Aristotle uses ousia.
Matters are even more complicated by the history of our English word substance,
which originates from the Latin translation of Aristotle's word for
subject, hupokeimenon, or underlying thing.
But don't worry about these linguistic complications if you find them
distracting.
I actually love this sort of thing.
The main point to keep in mind is that the term substance in
our translation of Aristotle is standing in for ousia,
which we can think of as the gold medal winner in the ontological olympics.
With this understanding of ousia, we can see that it has the ontological
status that Plato attributed to his intelligible forms.
So now we can articulate the ontological dispute between Plato and Aristotle.
Plato thought that the entities that deserve the title Ousia,
the most fundamental entities, are suprasensible, intelligible forms.
Aristotle, by contrast, thought that the most basic realities
are those that serve as subjects for all the rest.
And these are such ordinary entities as human beings, and other animals.