It turns out that it cannot, and this not merely because the answer has not yet been discovered, or because physics has not yet made sufficient progress, but rather because it is a category mistake to think that it could. This is the most fundamental objection to materialist naturalism as a comprehensive account of reality, a further discussion of which follows below. It should first be noted, however, that the conceptual and logical irrationalism of metaphysical naturalism is not its only problem; numerous scholars have pointed out other manifold difficulties. Nor should this be surprising insofar as the insufficiencies of dubious ideas usually disclose themselves in more than one way.
The first problem to be noted might not be insuperable for a scientistic reductionist fervently devoted to naturalism, but it would doubtless unsettle most human beings from all cultures, and rightly so. It is simply that if naturalism is true, there is no reason to think that there might be a basis for any objective ethical norms at all. There are only human constructions of morality, which shift according to cultural differences, historical processes, and individual preferences, subjectively overlaid by Homo sapiens sapiens on the purposeless substratum of matter-energy. There can be no question of anything actually being good or evil, right or wrong, just or unjust, because there are in reality no values, purposes, or meaning. To quote Christian Smith once again: «Matter and energy are not a moral source. They just exist and do what they do. The natural processes that govern the operations of the cosmos are not moral sources. They are simply the givens of physics and mathematics, elemental facts of natural reality lacking meaning or purpose or normativity... The evolutionary development of substances and life forms is not a moral source. They also just happen as they happen.»11 Nor is it apparent how any theories of emergence, which have been important in the natural and social sciences in recent decades and seek to explain how more complex realities and qualitatively different phenomena can arise from simpler constituent realities, could bridge the gulf between the complete absence and the objective presence of ethical norms.12 If naturalism is the truth about reality, then correlatively and obviously there could be no actual basis whatsoever for human rights, for example, nor any imperative to care about anyone or anything, or to act in certain ways rather than others; nor could there be any basis besides constructed preferences to condemn any behaviors, no matter how seemingly horrific from a conventional ethical perspective, including genocide, sex trafficking, or torture.
This is not strictly speaking a refutation of naturalism; some true believers might be willing to grasp this nettle despite its implications. Nietzsche, for example, seems to have understood that metaphysical naturalism entails ethical nihilism. But it seems apparent that we cannot really imagine any form of shared and sustainable, let alone desirable or appealing, human existence that would be compatible with many persons acting on such a view. Indeed, the longstanding project of trying to upgrade morality, as it were, by seeking to ground ethics in scientific findings, reflects both a recognition of the centrality of morality in human life and the hope that perhaps the empirical, rigorous methods of the natural sciences could overcome once and for all, with the same authority enjoyed by chemistry and physics, the ethical disagreements characteristic of human life and the divergences among moral philosophers apparent across cultures and throughout human history. This is what in recent years a number of different scientists and philosophers such as Patricia Churchland, Owen Flanagan, Joshua Greene, Jonathan Haidt, Alex Rosenberg, and others have been trying to do, combining in various ways a Humean sentimentalism, a Darwinian account of the evolution of the mind as an epiphenomenon of the brain, and the utilitarian ethical tradition that goes back to Jeremy Bentham and John Stuart Mill, rooting their efforts in an insistent, empirical naturalism. After an extensive review of these efforts, especially since the rapid rise of neuroimaging technology in the 1980s and 90s, and after considering relevant research in evolutionary biology, evolutionary psychology, primatology, neuroscience, and social psychology, the sociologist James Davison Hunter and philosopher Paul Nedelisky have concluded that even considered collectively, all of these efforts have provided «no clear empirical support for any moral theory, let alone for any claim about what is right and wrong, good or evil, or how we should live.»13
A second problem with metaphysical naturalism is different in kind – less disturbing in its practical implications for human coexistence, but more serious in strictly intellectual terms. It is not simply the inability of materialist naturalism to explain the phenomenon of consciousness in general, including more specifically human intentionality, cognition, and perhaps above all rationality, but also what multiple philosophers and even some scientists now regard as the impossibility of this explanatory aspiration in principle. Any and every attempt at a psychophysical reduction of first-person experiential awareness to nothing but neurophysiological and ultimately strictly physical processes has not only failed, but looks as though it is bound to fail. In 2011, the distinguished research physician and clinical neuroscientist, Raymond Tallis, a self-described atheist, argued at length in his book Aping Mankind that all attempts to reduce consciousness to nothing but brain functions have failed and cannot but fail.14 In 2012, one of the most distinguished analytical philosophers in the world, Thomas Nagel of NYU, unsettled the complacency of metaphysically naturalist colleagues committed to reductionist materialism with his short book, Mind and Cosmos, the subtitle of which is Why the Materialist Neo-Darwinian Conception of Nature is Almost Certainly False. Reviewers expressed shock and horror, appalled that Nagel acknowledged the influence on his thinking of Intelligent-Design critics of Darwinism, and risked giving comfort to religious believers even as he was apparently giving up on serious philosophy. Significantly, however, Nagel, like Tallis, is an atheist, and explicitly notes his disdain for theism.15 He simply does not see how materially reductionist accounts of physical processes alone, whether those currently available or any that might ever become available, could explain objective values (which he thinks are real), the experience of first-person subjective awareness (which is self-evidently and undeniably real), or the human capacity to rise above mere conscious sensation and perception to the comparative weighing of evidence and alternatives and the grasping of truth through rationality: «What has to be explained is not just the lacing of organic life with a tincture of qualia but the coming into existence of subjective individual points of view – a type of existence logically distinct from anything describable by the physical sciences alone» (44). Or again, «[j]ust as consciousness cannot be explained as a mere extension or complication of physical evolution, so reason cannot be explained as a mere extension or complication of consciousness» (81). In Nagel’s estimation, this implies that the entire evolutionary process must be rethought in such a way as to include non-material reality, because we know that the evolutionary process taken as a whole has produced the organisms we are: «materialism is incomplete even as a theory of the physical world, since the physical world includes conscious organisms among its most striking occupants» (45). This leads him to question the possibility of abiogenesis as a strictly physical process, presumably involving extremely complex protein folding and the formation of amino acids as steps on the way. How this or anything else might actually have led to self-replicating life is still a complete mystery but remains an important promissory article of faith among reductionists committed to what Nagel somewhat mischievously calls a «materialism and Darwinism of the gaps»: «no viable account, even a purely speculative one, seems to be available of how a system as staggeringly functionally complex and information-rich as a self-reproducing cell, controlled by DNA,