The composition of a substance

Start with this plausible observation:

1. Any part of me either is an accident of me or has an accident.

For consider this: my corporeal parts all have accidents of size, shape, color, etc. And my non-corporeal parts are my soul or form, as well as my accidents. My soul has accidents: such as the accident of thinking about this or that. And my accidents are my accidents.

Now, add this plausible thesis:

2. Any accident of a part of me is identical with an accident of me.

Thus, my arm’s being tanned is identical with my being tanned-in-the-arm. Further:

3. An accident of a thing is a part of that thing.

Given 1-3, we conclude the following:

4. Any part of me has at least one accident of me as a part.

For suppose that x is a part of me. Then by (1), x is an accident of me or has an accident. If x is an accident of me, then x has an accident of me, namely x itself, as an improper part. If x has an accident y, then y is a part of x by (3) and identical with an accident of me by (2), so once again x has an accident of me as a part.

Now the standard definition of composition is:

5. The xs compose y if and only if every part z of y has a part in common with at least one of the xs.

It follows from (4) and (5) that:

6. I am composed of my accidents.

For every part of me has one of my accidents as a part by (4), and that accident is of course an improper part of one of my accidents.

But (6) seems really wrong!

Thomas Aquinas has a nice way out of (6). One of my parts is my esse, my act of being, and my esse has no proper parts, and no parts in common with any of my accidents. If Aquinas is right, then it seems (4) needs to be modified to:

7. Any part of me is either my esse or has at least one accident of me as a part.

Replacing (4) with (7) in the argument, we get:

8. I am composed of my esse and my accidents.

But that seems wrong, too. For the omission of form is really glaring.

One could get out of (8) if one supposed that my form has its own esse as a part of it. But that doesn’t seem right.

My own view is that (8) may actually be correct if we stipulate “compose” to be defined by (5). But what that points to is the idea that “compose” is not rightly defined by (5).