Defenders Podcast: Doctrine of Man (Part 10)

Refuting Reductive and Non-Reductive Physicalism

Host: Dr. William Lane Craig
Date: July 23, 2025

Overview

This episode of Defenders continues Dr. William Lane Craig’s systematic study of the Doctrine of Man, focusing on philosophical challenges to physicalist (materialist) accounts of mind. Dr. Craig critiques both reductive and non-reductive physicalism, defending a dualist-interactionist view of human nature. The discussion draws on recent work in the philosophy of mind, particularly arguments by Angus Menuge, as well as observations about the increasing skepticism among contemporary philosophers regarding materialist theories of consciousness and selfhood.

Key Discussion Points & Insights

1. Defining Physicalism and Its Varieties

[00:16–04:00]

• Physicalism (Materialism): Asserts that humans are purely material beings with no immaterial (i.e., spiritual or mental) component.

• Reductive Physicalism: Mental states are identical with physical brain states; "there is just the brain and its physical states. All of our supposed mental states are reducible to brain states." – Dr. Craig [01:35]

• Non-Reductive Physicalism: Accepts that mental states aren't identical to brain states but holds that mental properties "supervene" on the brain (like "wetness" supervenes on H₂O), yet does not recognize an actual, ontologically distinct mind or soul.

  “All that really exists is the brain. But mental states or properties supervene on the material brain somewhat in the way that wetness supervenes on H₂O.”
  — Dr. Craig [02:35]

• Illustrative Example: The "wetness" of water to explain supervenience; only brain exists, but brain states give rise to mental properties.

2. Problems with Reductive and Non-Reductive Physicalism

[04:00–23:31]

A. Reductive Physicalism Fails to Account for Mental Life

[04:50–08:20]

• The brain as a physical object has properties like mass and shape, but not mental ones (sadness, joy, pain).

• Example: The brain is involved in the experience of pain, but “the brain itself isn't in pain.”

• Reductive physicalism cannot accommodate the qualitative (felt) nature of experiences (qualia).

  “You can't reduce fear to a physical brain state, even though it is correlated with neural activity in the brain. So reductive physicalism is obviously untenable. It cannot be reconciled with our mental experience.”
  — Dr. Craig [08:08]

B. Problems with Non-Reductive Physicalism

i. Incompatibility with Self-Identity Over Time
[09:10–13:18]

• No enduring self (“I”) in non-reductive physicalism; the mind is like the ever-changing flame atop a candle—there’s continuity, but no identical self persists.

• Rosenberg (naturalist philosopher): "the existence of the self... is an illusion." (see The Atheist's Guide to Reality)

• Without an enduring self, personal identity over time is denied.

  “If you do believe that you exist and that you are the same person who came into class this morning, then you ought to reject a non reductive physicalist view of the self.”
  — Dr. Craig [13:10]

ii. Intentionality (Aboutness) Is Incoherent
[13:18–17:40]

• Physical objects lack "aboutness"; only thoughts can be about something.

• Non-reductive physicalism, lacking a self, cannot account for intentional states.

• Rosenberg: “We never really think about anything... a sentence is just a bunch of ink marks on a piece of paper and therefore not about anything. They are just meaningless marks.”
  [Paraphrased from Dr. Craig summarizing Rosenberg, 15:10–16:00]

• Denial of intentionality is self-refuting: "An illusion is always an illusion of something."

  “An illusion of intentionality is an intentional state. You are having any illusion of something. So the view that intentionality is merely an illusion is literally self refuting and incoherent.”
  — Dr. Craig [17:18]

iii. No Room for Free Will
[17:40–19:40]

• Mental states cannot causally influence each other; all causality is physical and determined by laws of nature.

• Leads to determinism: “Free will is an illusion.”

• Yet, our experience as free agents seems undeniable.

  “If you believe that you ever do anything freely, then you have good reason to believe in the reality of the soul and to reject these reductive and non reductive views of physicalism.”
  — Dr. Craig [18:55]

iv. The Need for a Self in Reasoning
[19:40–20:45]

• Without a self, reasoning becomes comparable to meaningless calculations of a pocket calculator.
• “You ought to think that you are more than just a moist robot, that in fact you are a self who does this reasoning.”

v. Mental Causation & Neuroplasticity
[20:45–23:31]

• Non-reductive physicalism allows only one-way causation (from brain to mental states); mental states can't cause brain states.

• Neuroplasticity: Empirical evidence (e.g. effectiveness of cognitive therapy) that thinking can affect the brain.

  “If you think in certain ways, it produces brain effects. There is even a kind of cognitive therapy that in some cases is more useful than drugs in changing people's behavior.”
  — Dr. Craig [22:10]

• Rosenberg’s materialist 'solution' is to take Prozac; Dr. Craig: “we don't always need to resort to drugs. Sometimes... changing your thinking... will affect the patient physiologically.”

3. Implications and Discussion

[23:31–33:01]

• Neuroplasticity lends evidence to the soul's causal powers (audience comment, [23:31]).
• The move away from physicalism among philosophers is growing: “Physicalism is not as popular as it used to be.” — Dr. Craig [23:52]
• Association with Theism: Dualism fits better with a theistic view; "admitting the reality and existence of the soul... seems to open the door a crack for theism." [25:57]
• Even atheists might be more plausibly dualists, despite the uncomfortable fit: “It would be more plausible to be an atheist and a dualist, even though that is a very uncomfortable fit.” [26:08]
• Practical Contradiction for Naturalists: The unlivability of denying self, agency, and meaning—"every day you give the lie to your worldview." [27:33]

4. Physicalism and the Existence of Abstract Objects

[31:20–33:01]

• Challenge for materialists: what about logic, mathematics, abstract non-material realities?
• Willard Quine: Admitted abstract objects (mathematics, logic) were essential to science, yet remained a naturalist.
• Dr. Craig: "Even Quine... believed in... abstract objects. But how he could account for this sort of bifurcated view of reality, I don't know. He never did." [31:37]
• Platonic realism vs. anti-realism: Dr. Craig personally prefers anti-realism about abstract objects [33:19], but acknowledges the naturalist's tension in accepting any immaterial realities.

Notable Quotes & Memorable Moments

• On Reducibility:

  "You can't reduce fear to a physical brain state, even though it is correlated. So reductive physicalism is obviously untenable."
  — Dr. Craig [08:08]

• On Personal Identity:

  "If you do believe that you exist and that you are the same person who came into class this morning, then you ought to reject a non reductive physicalist view of the self."
  — Dr. Craig [13:10]

• On Intentionality:

  "An illusion of intentionality is an intentional state. The view that intentionality is merely an illusion is literally self refuting and incoherent."
  — Dr. Craig [17:18]

• On Free Will and Experience:

  "If you believe that you ever do anything freely, then you have good reason to believe in the reality of the soul and to reject these reductive and non reductive views of physicalism."
  — Dr. Craig [18:55]

• On Living Out Naturalism:

  "Even if you come to the belief that we have no free will, that I never think about anything, indeed, that I do not exist, you can't live that way. So every day you give the lie to your worldview."
  — Dr. Craig [27:33]

• On Dualism and Theism:

  “Admitting the reality and existence of the soul of an immaterial soul seems to open the door a crack for theism.”
  — Dr. Craig [25:57]

Important Segments & Timestamps

• Physicalism and its two main forms explained: [00:16–04:00]
• Limitations of reductive physicalism: [04:50–08:20]
• Problems with non-reductive physicalism (self-identity, intentionality, free will, reasoning, mental causation): [09:10–23:31]
• Discussion on neuroplasticity and its implications: [23:31–24:14]
• Dualism’s association with theism & practical tensions: [25:11–27:33]
• Materialist engagement with abstract objects (logic, mathematics): [31:20–33:01]

Conclusion

Dr. Craig argues powerfully that both reductive and non-reductive forms of physicalism are philosophically untenable. Drawing from both contemporary philosophy and scientific developments (like neuroplasticity), he contends that only a dualist account — where mind or soul is a real, causally active, immaterial entity — can adequately explain selfhood, intentionality, free will, rationality, and mental causation. Craig further highlights the existential and intellectual difficulties for naturalists who try to live consistently within a materialist outlook, concluding that dualism is not only more plausible but more livable — even if it opens the "door a crack" for theism.

For more resources from Dr. Craig:
reasonablefaith.org