Non-Reductive Physicalism—Overview

Non-Reductive Physicalism takes consciousness to be entirely physical, solely the product of biological brains, but mental states or properties are irreducibly distinct from physical states or properties such that they cannot be entirely explained by physical laws, principles, or discoveries (in brains or otherwise) (Macdonald & Macdonald, 2019).

Non-Reductive Physicalism was, in part, a response to conceptual problems in the early identity theories of physicalism, where mental properties or kinds were literally the same thing as physical properties or kinds. This was challenged by several conceptual conundrums: the multiple realizability of the same mental properties or kinds by different physical properties or kinds (Hilary Putnam); the intentional essence of mental phenomena, which seems so radically different from physical laws or things (Donald Davidson's “Anomalous Monism”); and the apparent unbridgeable gap between physics and the special sciences (Jerry Fodor) (Macdonald & Macdonald, 2019).

A core mechanism of Non-Reductive Physicalism is emergence, where novel properties at higher levels of integration are not discernible (and perhaps not even predictable, ever) from all-you-can-know at lower or more fundamental levels. A prime feature of Non-Reductive Physicalism is often “top-down causation,” where the content of consciousness is causally efficacious—qualia can do real work (contra Epiphenomenalism).

Religious Perspectives and Critiques

Some Christian philosophers, such as Nancey Murphy, who seek greater consonance between contemporary science and the Christian faith, look to Non-Reductive Physicalism as a nondualistic account of the human person. It does not consider the “soul” an entity separable from the body, such that scientific statements about the physical nature of human beings would be referring to exactly the same entity as theological statements concerning the spiritual nature of human beings (Brown et al., 1998). The structure of Non-Reductive Physicalism is said to enhance the Judeo-Christian concept of “resurrection of the dead” as opposed to what is said to be the non-Judeo-Christian doctrine of an “immortal soul” (Van Inwagen, 1995).

On the other hand, Christian philosopher J. P. Moreland takes dualism to be “the clear teaching of Scripture” that “overwhelmingly sets forth a dichotomy of soul and body,” and he decries those Christian thinkers who deny this conclusion, especially adherents of Non-Reductive Physicalism (Moreland, 2014).

Philosopher Jaegwon Kim's objections to Non-Reductive Physicalism, based on causal closure and overdetermination, highlight its three principles: the irreducibility of the mental to the physical; some version of mental-physical supervenience; and the causal efficaciousness of mental states. The problem, according to Kim, is that when these three commitments are combined, an inconsistency is generated that entails the causal impotence of mental properties (Kim, 2025).

Philosopher of science Nicholas Maxwell's Unique-Matching Theory posits a non-reductive, one-to-one, structure-preserving isomorphism between a multidimensional space of all possible sensations and a corresponding space of functionally described brain processes. His claim is that this structural necessity accounts for specific correlations between brain and consciousness without requiring reductive explanation (Maxwell's Unique-Matching Theory).

Comparison with Property Dualism

It is instructive to compare and contrast Non-Reductive Physicalism and Property Dualism. Both views are similar in their aim to explain the nature of consciousness in a world/universe/reality of only physical substances—there is only one kind of substance, the physical—but, in both views, crucially, mental states are not reducible to purely physical processes. That’s the similarity. The two views differ, perhaps significantly, in how they conceive the relationship between the mental and the physical—which impacts not only the deep nature of consciousness but also the deep nature of all reality.

Under Non-Reductive Physicalism, all substances and properties in the world/universe/reality are physical in nature, but mental properties are not reducible to lower-level physical explanations (like neurons or molecules). This means that while the physical gives rise to higher-level properties—mental states—that cannot be explained away by the lower-level properties. The mind emerges from brain processes, and while we can’t reduce beliefs and desires to neuronal impulses, they are still nothing over and above physical processes. In other words, mental properties are dependent on, caused by, and realized by physical states, but they are described at a different explanatory level. Emergence is key.

Under Property Dualism, there are two kinds of properties in the world/universe/reality: physical properties and non-physical (mental) properties. Everything (including brains) is made of physical substance, but mental properties (qualia, consciousness) are not reducible to or fully explainable by physical properties. Even if you know all the physical facts about brain activity, you wouldn’t know what it’s like to smell garlic cooking in olive oil unless you experience it—because the property of “garlic smell” as experienced is not physical. In other words, mental properties are fundamentally distinct from physical properties, though they may arise from physical systems. Consciousness has unique ontological status.

It would seem easy to blur, or admix, Non-Reductive Physicalism and Property Dualism in that both recognize real mental states and yet only one kind of substance (physical, material substance)—but each makes a very different fundamental claim. To reiterate, Non-Reductive Physicalism relies on the powers of physical emergence, while Property Dualism relies on consciousness having special ontological status.

I've always been puzzled by Non-Reductive Physicalism in that I can well understand how, under physicalism, consciousness is non-reductive in practice, but how non-reductive in principle? Conversely, if indeed consciousness is in principle non-reductive in the strong sense—impossible for science ever to explain how it works in terms of fundamental physical constituents—it would seem to require the ontological reality of non-physical properties (at least by current boundaries), which would seem to embed a contradiction. Or else, by what mechanisms could such higher-level non-reducible “laws” work? Perhaps by something analogous to quantum fields but operating at higher levels? Occam is sharpening his Razor.

C.D. Broad

Philosopher C. D. Broad is not classified here in the Non-Reductive Physicalism category, although he might well have been. He argued that phenomenal consciousness is real and irreducible: even complete physical knowledge of a brain could not reveal what an experience—such as smelling ammonia—feels like. His strong emergentism therefore held that consciousness may arise lawfully from complex physical organization while possessing genuinely novel qualitative properties. Broad systematically compared 17 possible mind-matter theories, favoring Emergent Materialism on ordinary evidence. However, taking psychical research seriously led him toward a Compound Theory in which consciousness might emerge from the conjunction of brain and a further “psychic factor.” Telepathy, precognition, mediumship, and survival evidence were therefore potentially crucial tests of whether consciousness exceeds normal neural constraints—possibilities Broad investigated rigorously but conditionally, without claiming paranormal phenomena established. Thus, Broad would have fit securely and comfortably in Non-Reductive Physicalism—were it not for his unusual turn bringing psychical research into the argument. Hence, he is classified in the Anomalous & Altered States category.