For now I want to comment on
three very common terms in the philosophy of science, two of which Nagel
employs in the first two chapters (reductionism and materialism) and one that
he does not (physicalism). It seems to
me that even very basic treatments of these topics frequently fail to
adequately define them, let alone get them right.
Reductionism comes in two very
different versions. Both versions posit
distinct levels of interpretation applying to the same phenomenon. For example, the human body consists of
organs that in turn consist of cells that in turn consist of molecules. Any organic action can be interpreted or
modeled at each level. The beating of
the heart can interpreted as the action of a pump. The contraction of the muscle can be
interpreted as the work of set of cells, etc.
Greedy reductionism involves
the view that the higher (which is to say more inclusive) levels are not
real. Only some lower, more fundamental
level, perhaps at the molecular or atomic level, is real. An analogy would be to the people on a TV
screen. The look to be real people but
this is an illusion; they are produced by pixels on the flat screen along with
the mechanics of the home video box you bought at Target.
The non-greedy version of
reductionism, entirely defensible in my view, is that the higher levels of
order are entirely composed of the simpler elements. My house key, for example, is entirely
composed of metal. The metal has its molecular
level at which the laws of chemistry and physics are rigorously enforced. Nonetheless, the key is real in both an epistemological
and a metaphysical sense. No knowledge
of the chemistry of metals would tell you what a key is, nor would the same
molecules be physical capable of opening my front door if the key were melted
down into a puddle of brass.
Materialism is a universally
abused term. It is usually taken to mean
that everything that is real is composed of matter. In those terms it is manifestly false, since
space and time and energy are all immaterial in nature even if they are
measured by a material apparatus.
However, the term materialism ought to confined, in my view, to a
certain doctrine about nature and natural change. A genuinely materialist explanation, such as
several Pre-Socratic philosophers attempted, would account for every
characteristic of a thing in terms of a specific type of material. Any change in a thing would be the result in
a change in the kinds and amounts of basic matter.
If a thing is both heavy and
shiny, that is because it has particles that present with those
characteristics, perhaps earth and fire as the ancients would sometimes have
it. The most famous example of a
genuinely materialistic explanatory scheme is the caloric theory of heat. Something becomes hot when it is saturated
with particles of heat, or caloric. If
you rest a hot stone on a table top for a bit and then remove it, a warm
impression will be left on the wood.
That is because the heat particles leaked out into the table top. I submit that only explanations of this kind
deserve to be called materialism.
By contrast, the molecular
theory of heat interprets the phenomenon as the level of energy at which the
molecules of a substance are moving relative to one another. That the same set of particles can display
different states is thus not a materialist explanation but a formalist one, to
coin a term. There is no doubt but that
materialist explanations have a big role in science, as anyone knows who is
familiar with the periodic table. There
is no doubt that materialist explanations alone are inadequate to explain all
but the simplest phenomena.
The third term is
physicalism. This is frequently used interchangeably
with materialism. It indicates the view
that nothing is real except what is physical.
But what does “physical” mean? Of
the three terms discussed here, this one seems to me to be the most neglected.
I offer a simple definition:
the physical is anything that is in principle measurable. Thus space, time, and all material objects
are physical. We can pull out the
measuring tapes, clocks, thermometers and scales to make a reading. Even if some characteristic is not
practically measureable (say the average temperature on some distant plant’s
atmosphere), it counts as physical in so far as we could imagine how to measure
it.
By my interpretation, physicalism
has a good claim to comprehend almost all the observable universe, if only
because of the fact that we can observe it.
The obvious exception is consciousness.
Modern science has all sorts of ways of measuring things that are
related to conscious awareness: brain activity, behavior, etc. We do not have any way to measure how
sincerely Brad loves Janet, nor do we have any idea how we could measure that
phenomenon directly. While we might
someday have such an idea, at present consciousness presents as something
non-physical.
That seems to be the point of
departure for Nagel’s argument.
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