Complex
Substance
A complex substance is an unordered whole that’s wholly built out of
substances. That is, it has only substances as parts. It is controversial whether
there are, or could be, complex substances. Part of the difficulty is in seeing
how to answer what Peter van Inwagen calls, ‘the special composition question’.
In my terminology, the question could be put this way: What is a principled way
to distinguish unordered wholes that are substance from mere arrangements (ordered wholes). Or to put it another way: what has
to happen to a bunch of substances for them to count as parts of a substance.
The various answers proposed, such as being in contact or being causally
connected, lead to counter-intuitive results (e.g., does the lollipop become a
part of your body when you touch it?)
For me, it is a wide open question whether there are
any complex substances. If there are, I suspect that they do not have any
separable parts—parts that could continue to exist even if separated. For if a
complex substance had separable parts, I would wonder what principle could
account for when a part is sufficiently
separated for it to no longer count as a part. For example, suppose that a
certain atom is presently A is part of my right toe T. T counts as a complex
substance of it can survive the loss of parts. Now suppose that T can lose A by
virtue of A becoming separated from T. A begins to move apart from the other
parts of T. Question: how far does A have to venture before A is no longer a
part of T. Either there is a precise answer to this question or there is not.
If there is not, then it is possible for the proposition that A is part of T to
be neither true nor false. (Notice I said proposition,
not sentence!) That is, bivalence would be false. Now many philosophers would
not be bothered by that result. But bivalence seems plausible to me (when
applied to propositions), and I have an independent reason to accept it in Chapter 3 of my dissertation on propositions and truth.
The alternative, then, is to say that there is a precise distance at which A is
no longer a part of T. But that strikes me as really odd—false even. Why should
the cut-off be right there rather than slightly higher or lower? It strikes me
that there should be an explanation, but I cannot see how there could be. All
this leads me to tentatively doubt or
be skeptical of the idea that there are complex substances with separable
parts.
Still, there is the option that there are or could
be complex substances that have no separable
parts. Perhaps some mental substances
would be like that if they were not built up out of material parts. Also, if every top-half of an extended thing
automatically has a top-half, then perhaps the smallest building blocks of
physical things are themselves complex substances that lack separable parts.
Final thought: philosophers sometimes talk about ontological priority when considering
the relationship between a complex thing and its parts. The usual thought is
that the parts of a thing are ontologically prior to it. But there is also the
thought that some wholes may be prior to their parts. I’ve sometimes wondered
if myself if quantum entanglement could be explained by virtue of a whole being
prior to its parts—so when you affect a part, you thereby affect the whole,
which in turn instantly affects the other parts. But then I find myself
suspicious of ‘priority’ talk. My first instinct is to see if the priority
relation can be analyzed into other more familiar relations, such as parthood,
epistemic priority, causation, entailment, or a combination of these. But maybe
there is an unanalyzable relation of ontological priority in addition to these
other asymmetric relations. One task of a metaphysician is to investigate which
things are prior to which other things (for various senses of prior).