Evolution of reductionism and its entanglement with materialism

How materialism and reductionism came to be widely seen as inseparable

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Reductionism—the idea that complex phenomena can be explained by reducing them to simpler components—has shaped the trajectory of modern science. Over time, it became tightly coupled with materialism (and its modern cousin, physicalism), forming a dominant paradigm for understanding the natural world. This article traces reductionism’s evolution, from its mechanistic roots to its contemporary reassessment.

The seeds of modern reductionism were sown in the 17th century during the Scientific Revolution. Thinkers such as Descartes, Galileo, and Newton envisioned nature as a vast machine governed by physical laws. Descartes’ Treatise on Man and Newton’s Principia both frame natural processes mechanistically, leaving little room for spontaneity or purpose. Their focus on quantifiable, mechanistic descriptions implicitly endorsed a reductive approach: understand the parts, and you can understand the whole.

At this stage, materialism—the view that only matter and its interactions exist—was not yet universally accepted. Descartes famously maintained a dualism between mind and body. Yet the mechanistic view of matter laid the groundwork for later materialist monism.

By the 18th century, Enlightenment thinkers began applying the mechanistic model to living systems. In La Mettrie’s Man a Machine (1748), humans were described as automata,¹ anticipating the reduction of mind to body. Here, materialism and reductionism began to converge: the physical world was seen as both sufficient and fully explanatory.

This trend accelerated in the 19th century as reductionism gained credibility through empirical success. In chemistry, atomic and kinetic theories linked chemical behavior to physical laws.² In biology, mechanistic physiology replaced vitalistic notions with explanations rooted in chemistry and physics. Meanwhile, Comte’s positivism urged science to discard metaphysical speculation and focus solely on observable phenomena,³ further cementing reductionism as a scientific virtue.

In the early 20th century, this attitude evolved into formal doctrines. Logical positivism, especially through the Vienna Circle, sought to express all scientific concepts in physical terms.⁴ This gave rise to physicalism—the doctrine that everything is ultimately physical. The momentum carried into psychology, where behaviorism aligned with the reductionist impulse by rejecting internal mental states in favor of observable behavior.⁵ Mental vocabulary was to be either translated into physical descriptions or eliminated.

In the mid-20th century, reductive materialism became dominant in the philosophy of mind. Identity theory held that mental states are brain states.⁶ On this view, consciousness was nothing more than neural activity. Yet tensions emerged. Functionalism, while still physicalist, allowed mental states to be realized in multiple ways—not strictly reducible to a single physical substrate.⁷ This opened the door to non-reductive physicalism, which preserved physical dependence while rejecting reduction.

By the 1970s, cracks in the edifice of universal reductionism were becoming evident. Advances in systems theory, emergence, and complexity began to challenge the reductive orthodoxy. In 1972, P.W. Anderson famously declared “more is different,”⁸ arguing that higher levels of organization introduce new laws that cannot be predicted from lower levels. Around the same time, philosophical critiques grew more pointed. Thomas Nagel’s 1974 essay What Is It Like to Be a Bat? cast doubt on the physicalism’s ability to account for subjective experience and sparked renewed interest in dual-aspect theories and property dualism.

The explanatory gap and the hard problem

In the 1980s and 1990s, two related arguments sharpened the challenge to reductive physicalism. Joseph Levine introduced the “explanatory gap” in 1983, arguing that even a complete neuroscientific account of pain leaves unexplained why those particular neural processes feel as they do.⁹ The gap is not merely a matter of current ignorance; it reflects a structural mismatch between the third-person language of physical science and the first-person reality of experience.

David Chalmers pressed the point further in 1995–96, distinguishing between the “easy problems” of consciousness—explaining cognitive functions, behavioral responses, and neural correlates—and the “hard problem”: why there is subjective experience at all.¹⁰ Chalmers argued that a zombie, physically identical to a conscious being but lacking inner experience, is at least conceivable, suggesting that consciousness is not logically entailed by physical facts. Whether or not one accepts the zombie argument, the hard problem crystallized a widespread intuition that reductive physicalism bears an explanatory burden it has not met. Non-reductive physicalism—the view that mental properties depend on physical properties yet are not reducible to them—gained traction as a way to respect both physics’ causal authority and the apparent irreducibility of consciousness.

Kim and the instability of non-reductive physicalism

Non-reductive physicalism seemed, for a time, a comfortable middle path: one could affirm that everything is ultimately physical while acknowledging that mental properties are real and irreducible. Jaegwon Kim dismantled this comfort through a sustained body of work culminating in Mind in a Physical World (1998) and Physicalism, or Something Near Enough (2005).

Kim’s central argument—the causal exclusion argument—rests on premises non-reductive physicalists accept. If mental properties supervene on physical properties (as non-reductive physicalism holds), and if every physical event has a sufficient physical cause (the causal closure of the physical domain), then mental properties appear to be causally redundant. The physical base already does all the causal work. The mental, as a distinct and irreducible layer, is left with nothing to do.¹¹

The logic is stark. Suppose a mental state M supervenes on a physical state P, and M is said to cause an effect E. Because the physical domain is causally closed, P is already sufficient to cause E. If M is not identical to P (as the non-reductive physicalist insists), then either M and P both cause E—systematic overdetermination, which Kim regards as implausible—or M is epiphenomenal, a causally inert shadow of the physical process. Neither option is what the non-reductive physicalist wants.

Kim concluded that non-reductive physicalism is an unstable position. Under pressure, it collapses into one of two alternatives: reductive physicalism, which preserves the mental’s causal efficacy by identifying the mental with the physical; or property dualism, which preserves the mental’s distinctness but abandons the causal closure principle.¹² What it cannot coherently do is maintain all three commitments—supervenience without identity, causal closure, and genuine mental causation—simultaneously.

The significance of Kim’s critique extends beyond the technical philosophy of mind. It shows that the dominant middle-ground position in late 20th-century philosophy was not, in fact, stable ground. The options are starker than non-reductive physicalism suggested: either consciousness reduces without remainder to physical processes, or the physical domain is not causally closed as physicalism requires. The comfortable middle is an illusion.

The contemporary landscape

Many now distinguish ontological physicalism (everything is physical) from methodological reductionism (everything should be explained in terms of physics). In practice, methodological reductionism remains a powerful tool. Neuroscience and its allied disciplines successfully account for a wide range of phenomena.¹³ Yet methodological success does not entail the ontological conclusion that everything is physical. Dual-aspect monism, idealism, and even panpsychism are also fully compatible with these findings and are gaining traction as alternatives.¹⁴

Reductionism emerged as a powerful method for understanding nature by breaking it down. Over time, it evolved into a metaphysical commitment—closely linked to materialism and physicalism. Today, its role is more nuanced. Reduction remains a useful strategy, but its claim to exclusivity is increasingly challenged by those who argue that mind, meaning, and value resist being fully captured by lower-level physical explanations. The trajectory from Nagel through Levine and Chalmers to Kim traces an arc of deepening pressure: the explanatory gap reveals what reductive physicalism cannot explain; the hard problem clarifies why it cannot; and the causal exclusion argument shows that the most popular alternative—non-reductive physicalism—cannot hold its ground coherently.

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1. .↩︎

2. ↩︎

3. Comte, Auguste. Cours de philosophie positive (1830–42).↩︎

4. ↩︎

5. Watson (1913) and Skinner (1938) sought to eliminate subjective states from scientific psychology.↩︎

6. Smart, J.J.C. “Sensations and Brain Processes” (1959); Place, U.T. “Is Consciousness a Brain Process?” (1956).↩︎

7. Putnam and Fodor proposed functionalist accounts in the 1960s–70s.↩︎

8. Anderson, P.W. “More is Different.” Science, 177(4047), 393–396 (1972).↩︎

9. Nagel, Thomas. “What Is It Like to Be a Bat?” Philosophical Review, 83(4): 435–450 (1974)↩︎

10. Levine, Joseph. “Materialism and Qualia: The Explanatory Gap.” Pacific Philosophical Quarterly, 64(4): 354–361 (1983).↩︎

11. Chalmers, David J. “Facing Up to the Problem of Consciousness.” Journal of Consciousness Studies, 2(3): 200–219 (1995). Expanded in The Conscious Mind (1996).↩︎

12. Kim, Jaegwon. Mind in a Physical World: An Essay on the Mind-Body Problem and Mental Causation. MIT Press, 1998. See especially chapters 2 and 4.↩︎

13. Kim, Jaegwon. Physicalism, or Something Near Enough. Princeton University Press, 2005.↩︎

14. See Chemero, A. Radical Embodied Cognitive Science (2009) for a critique of reductionist cognition.↩︎

15. Goff, Philip. Galileo’s Error (2019) offers a defense of panpsychism in response to reductive failures. Also: Skribina, David. Panpsychism in the West (2007) for an historical account of panpsychism and how it should be seen as a meta-theory of mind rather than a specific framework.↩︎

1. La Mettrie, Julien Offray de. L’Homme Machine. 1748

2. Dalton’s atomic theory (1808) and later developments in thermodynamics provided inter-theoretic reductions: chemistry explained via physics.

3. Comte, Auguste. Cours de philosophie positive (1830–42).

4. Carnap, Neurath, and others proposed the “Unity of Science” thesis: all sciences are reducible to physics through bridge laws.

5. Watson (1913) and Skinner (1938) sought to eliminate subjective states from scientific psychology.

6. Smart, J.J.C. “Sensations and Brain Processes” (1959); Place, U.T. “Is Consciousness a Brain Process?” (1956).

7. Putnam and Fodor proposed functionalist accounts in the 1960s–70s.

8. Anderson, P.W. “More is Different.” Science, 177(4047), 393–396 (1972).Nagel, Thomas. “What Is It Like to Be a Bat?” Philosophical Review, 83(4): 435–450 (1974)

9. Levine, Joseph. “Materialism and Qualia: The Explanatory Gap.” Pacific Philosophical Quarterly, 64(4): 354–361 (1983).

10. Chalmers, David J. “Facing Up to the Problem of Consciousness.” Journal of Consciousness Studies, 2(3): 200–219 (1995). Expanded in The Conscious Mind (1996).

11. Kim, Jaegwon. Mind in a Physical World: An Essay on the Mind-Body Problem and Mental Causation. MIT Press, 1998. See especially chapters 2 and 4.

12. Kim, Jaegwon. Physicalism, or Something Near Enough. Princeton University Press, 2005.

13. See Chemero, A. Radical Embodied Cognitive Science (2009) for a critique of reductionist cognition.

14. Goff, Philip. Galileo’s Error (2019) offers a defense of panpsychism in response to reductive failures. Also: Skribina, David. Panpsychism in the West (2007) for an historical account of panpsychism and how it should be seen as a meta-theory of mind rather than a specific framework.