In Chapter Four of Mind
and Cosmos: Why the Materialist Neo-Darwinian Conception of Nature Is Almost
Certainly False, Thomas Nagel turns to the mystery of human
reason. Before I comment, I will
consider Aristotle’s tripartite model of the soul, from On the Soul.
For Aristotle, the soul is the
actuality of an organic body that has the potential for life. To understand this concept, consider the
question “What is a church?” Is it
bricks, boards, plumbing, and pews?
No. Empty of people, it is merely
a structure with the potential of being a church. Is it the people who show up on Sunday? No. If
the same people occupy the same building but are engaged in gambling and
whoring, then it is a casino and a brothel, rather than a church. The church is these people collectively
worshiping. Likewise, the soul is this
material organized into, well, organs, and doing the things that living things
do. What do they do?
The most basic activities that
characterize a soul are absorbing nutrients and producing waste. If it eats and goes potty, it’s alive. An essential character of soul is a dimension
of value. A being with a soul can
survive and flourish or wither and die.
It can succeed or fail, something in which no rock is involved.
This basic level of soul has
been dubbed nutritive soul. Aristotle thought that all living things have
this kind of soul, but plants had this alone.
In addition to nutritive soul, animals have the capacity to move about
and perceive at a distance. Animal soul
opens up a second existential dimension: pain and pleasure. Apart from flourishing and withering (though
to be sure, connected with the same) animals can have good and bad lives.
Finally there is a third type
of soul possessed by human beings alone.
In addition to nutritive soul and animal soul, human beings have logos.
An animal cannot distinguish between what it perceives and what is
true. Accordingly, no animal can distinguish
between what it wants and what is good for it.
Human beings can make these distinctions, and that makes all the
difference.
Aristotle’s scheme is
astonishingly easy to map onto an evolutionary account of the emergence of
complex organisms. Evolution does not replace
simple forms with more complex ones.
Instead, it lays increasingly complex levels of organization on top of
earlier ones. Plants communicate within
their bodies by the movement of fluids. Animals
do the same, but over those mechanisms are laid a system of nerves coordinated
by a brain. Human beings are
animals. Our capacities are laid on top
of the capacities enjoyed by other mammals.
Are we more than animals? An obvious challenge to Aristotle is to say
that he privileges human beings. Isn’t
our logos just a more sophisticated device for running the gauntlet of
reproductive success? Maybe.
Nagel seems to agree with
Aristotle that our rational capacity puts us in an entirely new category and
that our reliance on reason cannot easily be explained in evolutionary
terms. More on that later.
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