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Sean Carroll: “How Could an Immaterial Mind Affect the Body?”

The well known physicist thinks free will is nonsense. But has he investigated the classical understanding of causation?

Sean Carroll is a theoretical physicist at Johns Hopkins University who takes an atheist and materialist philosophical perspective on nature and on science. I have disagreed with him often — I’m in no position to judge his scientific acumen, but his philosophical acumen leaves a lot to be desired. An example of this is a question he asks in a recent documentary about free will (which I haven’t watched yet). In the trailer for the movie, Carroll asks, How in the world does the immaterial mind affect the physical body?

Carroll’s denial of libertarian free will is based on this question, and of course, he believes that the immaterial mind does not exist and, if it did exist, could not affect the physical body. Thus, he believes that libertarian free will is nonsense.

Carroll’s Error and Aristotle’s Four Causes

Carroll’s error here is his presumption that all causation in nature is truncated material and efficient causation. A brief review of the classical Aristotelian understanding of causes in nature is helpful here in seeing where Carroll goes wrong.

Aristotle noted that when we think carefully about natural causes we see that there are four distinct ways that causes can lead to effects in nature. We use a statue as an example of an effect whose causes we can study:

  1. Material cause is the matter (marble) that the statue is made of. The matter of what something is made is one of the causes of the thing – without the marble, the statue could not exist.
  2. Efficient cause is the agent that gives rise to the effect – in the case of the sculpture, the efficient cause is a sculptor.
  3. Formal cause is the design principle that underlies the effect – in the case of the sculpture, the formal cause is the idea in the mind of the sculptor of what the sculpture will look like. The formal cause is quite real and is indispensable to an understanding of causation – after all if the form of the sculpture did not exist in the mind of the sculptor as he was working, there would be no sculpture.
  4. Final cause is the ultimate goal, purpose, or final state of the causal chain. The final cause for the sculpture might be the sculptor’s desire to express himself artistically or it might be the sculptor’s desire to be paid for his work.

In the Aristotelian paradigm, a complete understanding of cause must entail an understanding of all four causes in nature. In causation without a visible efficient agent, formal and final causes are often the same. The formal cause of an acorn growing into an oak tree is the design principle of the oak tree, which is also (in the Aristotelian perspective) the final cause of the acorn growing into the oak tree. The ultimate final cause, according to Aristotle, is God.

An Immaterial Cause is Necessary

Francis Bacon in the 17th century proposed that Aristotelian formal and final causes were irrelevant to a scientific understanding of nature, and since Bacon’s time, formal and final causes have been relegated to obscurity. But Aristotle was right – material and efficient causes alone are inadequate to understand nature because there are patterns and purposes built into nature that we can’t deny.

So, Carroll’s implicit assertion that the immaterial mind could not affect the physical body is predicated on his belief that the only kinds of causes that exist in the physical world are material and efficient causes. He is wrong about that. Ironically, Carroll’s own scientific discipline – quantum mechanics – is a prime example of the importance of formal causes in nature. The scientific description of quantum processes is entirely mathematical, which is a description of formal causes. Matter and individuation disappear at the quantum level. What remains are the mathematical descriptions of quantum particles and dynamics. Contrary to Carroll’s implicit insistence that only material and efficient causes act in nature, quantum mechanics shows that formal (immaterial) causes are fundamental to nature.

Thus a mental (formal) state can cause a physical state in a way that is currently understood in physics. A particularly striking example of the importance of formal causes in science is the phenomenon of chirality. Chirality is a property of mirror image molecules in which the molecules contain exactly the same number and kinds of atoms connected in exactly the same kind of way except that one is a mirror image of the other. In other words, the matter comprising chiral molecules is exactly the same although the form of the molecules can be radically different. For example, all biological amino acids that make up proteins are L enantiomers (one mirror image). Amino acids that are identical materially but are R enantiomers (mirror images) play no role in protein manufacture. The difference between L and R enantiomers can be a matter of great medical importance and even life and death – Darvon is an analgesic but its enantiomer Novrad is an anti-cough agent. Penicillamine is used in the treatment of arthritis, but its enantiomer is very toxic.

The Longstanding Basis for Free Will is Substantial

Formal causation is ubiquitous in biology and Carroll’s argument that we cannot have libertarian free will because the immaterial (formal) mind cannot affect matter is philosophically vacuous. Libertarian free will in this paradigm is an example of the action of formal and final cause on brain matter – the intellect (formal cause) provides an understanding of the choices and the will (final cause) provides a decision on how to act. Contra Carroll, there is a 2000-year tradition of understanding immaterial formal and final causation in nature that provides a substantial metaphysical and scientific basis for the observation that libertarian free will is real.

Michael Egnor

Senior Fellow, Center for Natural & Artificial Intelligence
Michael R. Egnor, MD, is a Professor of Neurosurgery and Pediatrics at State University of New York, Stony Brook, has served as the Director of Pediatric Neurosurgery, and award-winning brain surgeon. He was named one of New York’s best doctors by the New York Magazine in 2005. He received his medical education at Columbia University College of Physicians and Surgeons and completed his residency at Jackson Memorial Hospital. His research on hydrocephalus has been published in journals including Journal of Neurosurgery, Pediatrics, and Cerebrospinal Fluid Research. He is on the Scientific Advisory Board of the Hydrocephalus Association in the United States and has lectured extensively throughout the United States and Europe.

Sean Carroll: “How Could an Immaterial Mind Affect the Body?”