Natural Philosophy - Substance and Accident
What the meaning of "IS" is First, as a kind of preliminary and as tool for philosophical discourse, one should be familiar with the basic distinctions of Aristotle's logic. The basic logical distinction for our purposes is between accident (what exists in and is said of another) and substance (what does not exist in another & not said of another). As an example of what Aristotle means, consider what is named by the word "white." The reality that this word names (a particular color) can be said of some other thing as eg. "This thing is white." "White" is said of "this thing" as though the color belonged to "this thing." Furthermore, it is understood to exist in "this thing;" one does not find any "white" except that is in "this thing" or some other thing. This way of speaking can be contrasted with another, as for example "This thing is Socrates." "Socrates" does not name the same kind of reality that "white" does in the previous example. "Socrates" is not said of "this thing" in the same way as "white" is, and "Socrates" does not exist IN "this thing." Rather, "Socreates" IS "this thing," and the sentence "this thing is Socrates" is understood to assert an identity between the two realities named.
This basic notion of Aristotle's logic reflects the basic distinction in the way reality is stuctured and reflects the basic way that we view reality. The fundamental distinction is between substance and accident. Substance is whatever is a natural kind of thing and exists in its own right. Examples are rocks, trees, animals, etc. What an animal is, a dog for example, is basically the same whether it is black or brown, here or there, etc. A dog is a substance since it exists in its own right; it does not exist in something else, the way a color does.
Substance and Accidents
Accidents are the modifications that substance undergo, but that do not change the kind of thing that each substance is. Accidents only exist when they are the accidents of some substance. Examples are colors, weight, motion. For Aristotle there are 10 categories into which things naturally fall.
They are
Substance,
and
Nine Accidents:
Quantity,
Quality,
Relation,
Action,
Passion,
Time,
Place,
Disposition (the arrangement of parts), and
Rainment (whether a thing is dressed or armed, etc.)
All these distinctions are basically logical, but in a sense they reflect the structure of reality. One never finds any substance that we experience without some accidents, nor an accident that is not the accident of a substance. Every dog, for instance, has some color, place, size. Nevertheless, it is obvious that what a dog is is not the same as its color, or its size, etc.
from:http://www.aquinasonline.com/Topics/index.html
