Non-Mental
Substance
A non-mental substance is a substance that lacks mental properties, properties
like feeling sad or being aware of a proposition. A simple non-mental substance would be a non-mental substance that
lacks parts.
The study of non-mental substances, of their
behaviors and properties, is the domain the natural sciences. Mathematicians
study the properties of the properties
of non-mental substances. For example, geometers study the properties of the shapes of non-mental substances. (I actually
accept Euclid’s five postulates of geometry, including the parallel postulate. I
view non-Euclidean geometry as a logic of conditional propositions of the form if the parallel postulate were false, then… Since
the parallel postulate is true in my view, non-Euclidean geometry doesn’t give
us any direct insight into reality beyond the reality of those conditionals. I
realize this is not a popular view, but I think it’s the right one.) Number
theorists study the properties of quantities
or measures of degrees of various properties of non-mental substances, such
as degree of velocity or acceleration. Calculus studies properties of change in degrees of various properties
of non-mental substances, like change in location or momentum. I view Algebra as
a logic (a study of “truth flow”) of propositions about geometry, calculus, and
number theory.
Philosophers of space, time, and causation may also
contribute to our understanding of non-mental substances. However, the most useful facts about the non-mental tend
to be contingent ones—ones having to do with what non-mental things there are.
And philosophers don’t usually investigate contingent facts. They are better at
investigating the necessary constraints on contingent facts (metaphysics) and
on the nature of our inquiry into them (epistemology).
Still, there are questions about non-mental
substances that may interest philosophers. Consider these:
(1) Must
every spatially extended substance have a top-half?
(2) Can
a non-mental substance move without being determined
to do so by its nature?
(3) Can
a non-mental substance affect another non-mental substance without touching or
overlapping it?
(4) Can
two non-mental substances spatially over-lap?
There are many other questions, too, and an
important project for truth-seekers is to rank such questions in order of importance.