This post is one in a series about naturalism. Having introduced the general concept of naturalism and one popular form I call Thomistic naturalism, I turn to a more recent version common in the general public. From “Naturalism I”:
Naturalism is a universal claim about what we can meaningfully talk about.
Sometime around the 16th and 17th century, Western civilization made a radical shift in philosophy from the medieval scholastic perspective to a new worldview. That picture would be less religious, strongly empirical, and conducive to the rise of modern science. It rests on the contributions of countless thinkers, but received a strong push from Rene Descartes (1596-1650). Like Thomas Aquinas, he divided the world up into parts, but he did so along very different lines.
Descartes felt that some things could be known by looking inward. The most famous such statement was cogito ergo sum, I think therefore I am. Descartes felt this was the one truly solid foundation upon which one could build knowledge of the universe – the subjective experience of reasoning. He thought his mind, and by extension God and other minds, must exist as a prerequisite for reasoning about the universe. This mind was not a physical process, but something ideal and abstract, capable of reliable reasoning.
The Cartesian perspective, particularly as it comes to us through Hume and Kant, makes claims about our ability to generate knowledge. This Enlightenment perspective holds knowledge to be “justified true belief” Let me break that down. A belief is a proposition resident with the mind, generally a claim about the world. True refers to a relationship between the proposition and reality – a true belief about the world agrees with the way the world actually is. Justified means that we have adequate rational grounds for thinking the belief is true. It’s not sufficient to guess and just happen to be right. Enlightenment thinkers wanted certainty that they were right, so they developed laws of inference, including deduction (irrefutable arguments from one belief to another) and induction (suggestive arguments from one belief to another). Remember, he started with the single belief – I exist – and had to work his way up from there.
For Descartes, the mind was more real than the physical world (or at least more accessible). We could use deduction mentally to produce knowledge, but only use induction based on our senses to generate beliefs about material things. This dual perspective would be refined over the next few centuries and gradually became more confident of knowledge about the physical world. We never lost, however, the idea that beliefs can only be truly justified in the mind. Any time we say that physical processes, rather than rational (mental) processes, have “caused” a belief, we are really claiming that it cannot be true knowledge. For instance, I might say “you only hear a ringing because you hit your head.” Physical causation of belief is considered almost universally to defeat the claim that the belief constitutes knowledge. The separation of the mental realm allowed Descartes to claim certainty – mind need not be corrupted by the chain of physical causation.
In order to simplify the problems of physical knowledge, it was assumed the the physical world operated in a mechanical way based on discrete physical particles and universal laws. This simplification was effected by, quite transparently, moving all the difficult bits out of the physical universe. The hard problems of science presented by Aristotle – sensation, motivation, and reason – were moved out of the physical realm and into the mental realm, with no clear method for communication between the two. This leads to what I call the “awkward patch” of the mechanical philosophy. “Minds” or souls were invoked to explain what it was that sensed the physical world, felt emotions, had ideas, and caused actions. Existing in a parallel reality, minds, in some mysterious fashion, did the work necessary to provide what we think of as external experience so that everything else could be explained mechanically.
A special case of mind was invoked under the heading of “God” to explain how the whole machine was wound up in the first place, where the particles and laws came from, where the minds came from, and how they communicate.
Curiously, the hard problem of nutrition was basically declared a non-problem. Living bodies were thought to be nothing more than machines unless mysteriously inhabited by souls. Hence, “the ghost in the machine” only applies to human machines. Aristotle saw plants and animals as vacant clockwork devices.
The two most common uses of natural in modern English refer to the two aspects of the awkward patch. We most often use natural to mean the opposite of artificial. We speak of a “state of nature” in order to describe something that has not been changed due to human intent, the imposition of rational intent from the realm of minds.
As an evolutionary biologist, I’ve always found it curious that we call human agriculture “artificial selection” (breeding) while we call ant agriculture (ants herd aphids and culture fungus) “natural selection.” In both cases we see imposition of the needs of one species on another, distantly related species. Only human interference, however, is classed as artificial. The distinction comes from the Cartesian belief that humans, uniquely, possess this mysterious link to the realm of minds.
The second use of natural sets it opposed to the being and actions of God. Hence, natural versus supernatural.
Cartesian naturalism claims that the simplified physical realm of Descartes is sufficient to understand everything. Neither minds nor God need be invoked. Remember, by mind, I do not mean the operation of the brain. I mean the non-physical entity that can reason perfectly without interference from physical causes. I mean the locus of sensation and source of action that mysteriously communicates with human bodies.
I find Cartesian naturalism compelling precisely because it so succinctly manages to explain so many physical phenomena in terms of particles and forces. It is blessedly simple. Of course, Descartes only achieved that simplicity by moving the tricky bits to another realm of existence where they would have the objectivity to achieve true knowledge, a subject I will take up in more detail shortly. Thus Cartesian naturalism only works for me when paired with Cartesian rationalism, the rules for the mental realm. It can only be a relative claim about the physical world and not a universal claim about all of reality.