Defenders Podcast: Doctrine of Man (Part 11): A Challenge to Dualism-Interactionism – The Libet Experiments

Host: Dr. William Lane Craig
Date: July 30, 2025

Episode Overview

In this episode, Dr. William Lane Craig delves into a significant challenge to dualism-interactionism presented by the famous Libet experiments in neuroscience. He addresses how these experiments are often interpreted as undermining free will and dualist perspectives, then offers a robust philosophical and scientific defense of dualism-interactionism. In the latter half, Dr. Craig briefly discusses the question of whether human beings are dichotomous (body and soul) or trichotomous (body, soul, and spirit).

Key Discussion Points & Insights

1. Context & Challenge: The Libet Experiments (00:17–02:00)

• Dr. Craig introduces the challenge to dualism-interactionism coming from Benjamin Libet’s experiments, where brain signals were measured during voluntary finger movements.
• Three key events in Libet’s findings:
  1. Brain signal (readiness potential) occurs ~550 milliseconds prior to finger movement.
  2. Subject becomes consciously aware of the decision ~200 milliseconds prior to finger movement.
  3. Finger moves to press the button.
• Interpretation: Some argue these results favor determinism/materialism, suggesting the brain "decides" before conscious awareness.

"What Libet discovered was that prior to a person’s awareness of his decision...a brain signal had already occurred which later resulted in his fingers moving..." (B, 00:30)

2. Critique of Deterministic Inference (02:01–04:00)

• Dr. Craig explains that it is “overdrawn” to claim these findings prove determinism or materialism.
• Libet’s second set of experiments shows that even after becoming aware of the decision, subjects can veto the action, exercising control over the outcome.

"The bottom line is that the person still has control over his decision. Libet himself considered his experimental results to be fully compatible with the existence of free will." (B, 03:00)

3. Dualist-Interactionist Interpretation (04:01–09:30)

• Dr. Craig argues this time lag is not problematic but expected on dualist-interactionism.
• Cites Sir John Eccles: The soul uses the brain as an instrument, much like a pianist uses a piano; thus, their actions are not instantaneous.
• Due to the finite velocity of neural signals, conscious awareness lags behind the actual decision.

"Given the brain’s reliance upon finite velocity neural signals in order to think, the soul could not have a simultaneous awareness of its decisions...there has to be a time lag between the soul’s decision and the soul’s conscious awareness of that decision." (B, 05:30)

• Analogy: Just as we always perceive things a bit in the past due to the finite speed of light and sound, so too there’s a delay in conscious awareness of decisions.
• Fundamental Point: Dualist-interactionists should expect a small time lag and it does not contradict the soul’s free will or agency.

4. Philosophical Support: Uwe Meixner’s View (09:31–11:00)

• Dr. Craig quotes philosopher Uwe Meixner, reinforcing that being conscious of facts before making a decision is what’s necessary, not simultaneous awareness of the act of deciding.
• Meixner’s Key Insights:
  • Consciousness of an event always lags slightly behind the event itself due to reliance on neurophysiology.
  • This general rule applies to decisions as well.

"For making an informed decision, the self needs to be conscious of the facts relevant to the decision and prior to making the decision. But the self does not need to be conscious of making the decision at the very same time..." (B quoting Meixner, 09:50)

5. Why the Libet Findings Support Dualist-Interactionism (11:01–12:35)

• The soul’s decision is not unconscious, just slightly delayed in conscious awareness.
• The time lag is inherent to the finite speed of neurophysiological processes, mirroring our sense perceptions.
• Conclusion: Libet’s findings fit perfectly with what dualism-interactionism predicts.

"If, therefore, the soul has the ability to think without being causally determined...all it needs to do in order to make responsible, informed, free decisions is consciousness of the relevant facts prior to its making a decision." (B, 11:40)

6. Dichotomy vs. Trichotomy in Human Composition (12:36–13:45)

• Briefly addresses the traditional debate: Are humans composites of body and soul (dichotomy), or body, soul, and spirit (trichotomy)?
• Dr. Craig believes trichotomy risks “multiplying entities unnecessarily” and notes scripture, if pressed, would also force us to consider “heart,” “mind,” and “inner man” as additional entities.
• Advocates for a functional, not ontological, distinction: the soul as it relates to God is called 'spirit'; the same soul, as rational agent, is called 'soul'.

"It seems to me that there isn’t any sort of strong and consistent distinction in scripture or philosophy that can be drawn between the soul and the spirit..." (B, 13:00)

"So we do have a spiritual dimension to our lives...but I don’t think that needs to be cashed out in terms of saying that there is an additional thing of which we are composed..." (B, 13:35)

Notable Quotes & Memorable Moments

• On brain signals and awareness:
  "So the sequence of events goes like this. Number one, there is a brain signal about 550 milliseconds prior to the fingers moving. Two, there is an awareness of the decision in consciousness which occurs about 200 milliseconds prior to the fingers moving." (B, 00:48)
• Libet himself on free will:
  "Libet himself considered his experimental results to be fully compatible with the existence of free will." (B, 03:13)
• The soul uses the brain as an instrument:
  "The soul uses the brain to think as an instrument for thought, just as a pianist uses a piano as an instrument to produce music." (B, 04:48)
• Uwe Meixner’s analogy:
  "The consciousness of a state of affairs...is always somewhat later than the actual fact..." (B quoting Meixner, 09:58)
• Functional—not ontological—distinction:
  "The soul insofar as it functions in relation to God can be called the spirit...I think it's best to see the difference between soul and spirit as a functional difference." (B, 13:20)

Timestamps for Key Segments

• 00:17 – Introduction to Libet’s experiments and the challenge to dualism
• 02:00 – Libet’s findings and deterministic/materialist interpretations
• 03:00 – The significance of the veto power in Libet’s experiments
• 05:30 – Explanation of the dualist-interactionist view and neural signal delays
• 09:50 – Uwe Meixner’s philosophical perspective
• 12:36 – Dichotomy vs. trichotomy in human composition

Tone and Approach

Dr. Craig’s tone is calm, methodical, and pedagogical, often using analogies from everyday life and science to clarify philosophical points. His approach is reasoned and charitable to alternative interpretations but remains resolutely dualist-interactionist in his explanations and theological commitments.

Next Episode Teaser: Discussion will move to the topic of the origin of the soul.
Reminder: Dr. Craig encourages listeners to stay safe during the pandemic and to continue exploring philosophical and theological questions.