Aristotle offers us an account of reality as a whole.
In order to understand his account of reality as a whole, we need to understand what he
means by the terms substance and accident.
So let's take a moment to consider these terms.
It is important to pause with these terms since they have quite different meanings in
their philosophical and Thomistic usage than they have in ordinary language.
In ordinary language, a substance is any sample of stuff.
Students in a chemistry lab, for example, will speak of various substances that they're
weighing or burning or experimenting with.
In ordinary language, accidents are events that happen unintentionally or by chance,
such as falling down the stairs or being rear-ended on the way to work.
But these terms, substance and accident, have completely different meanings in the philosophical
tradition and especially in the usage of Thomas Aquinas.
For Saint Thomas, substance may refer either to a particular existing thing or to the substantial
form of a particular existing thing.
A particular dog such as Fido is a substance, but so too is the form of Fido or his essence,
which is that of being a dog.
That too is called a substance.
We understand substance by contrast with accidents.
Accidents are the features or traits of substances, such as the weight or color or actions of
a thing.
Fido, for example, may weigh 10 pounds and have brown fur and bark.
These are accidents of Fido.
According to Aristotle, and Thomas Aquinas follows him in this, accidents do not exist
except in various substances, and substances are the realities underlying and displaying
all those accidents.
They're called substances because they stand under--substand--accidents.
Substances do not exist in other things but exist on their own, but it is very important
to qualify this up front.
We are not saying that substances exist independently of God.
Aquinas has a metaphysics of participation which tells us that all substances other than
God participate in the very being of God.
When it is said that substances are independent or exist on their own, this is said by contrast
to accidents.
It is not said with reference to God.
It is also important to note that for Aristotle and Thomas Aquinas, substances are not inert
or static entities.
Whatever exists is active, and the more being a thing has, the more active it is.
Accidents are active and substances are even more active than the accidents they underlie.
The world is not a place of static individuals, but of active realities.
Thomas Aquinas thought that all of reality could be classified according to the distinction
between substance and accident.
Whatever exists is either a substance or an accident.
Aristotle found nine kinds of accidents in things: qualities, quantities, relations,
time, place, action, passion, position and habit.
The substances and these nine accidents, together, are famously called the 10 categories.
Every finite being whatsoever belongs to one of these 10 categories, but God transcends
them all since he is infinite.
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