Wednesday, December 12, 2012

Aristotle's Soul, Evolution, & Logos

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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