Ontological Naturalism and Nihilism
Here is a short argument that ontological naturalism (ON) is either antirealist/nihilist about value or that it is axiological neutral.
First, I provide some working definitions. Roughly, ON holds that reality is nothing but the spatiotemporal realm of physical objects. As David Papineau puts it, “a central thought in ontological naturalism is that all spatiotemporal entities must be identical to or metaphysically constituted by physical entities. Many ontological naturalists thus adopt a physicalist attitude to mental, biological, social and other such “special” subject matters. They hold that there is nothing more to the mental, biological and social realms than arrangements of physical entities [my emphasis].”[1] And as David Armstrong notes, ON is “the doctrine that reality consists of nothing but a single all-embracing spatio-temporal system.”[2] Axiological antirealism (i.e., nihilism) is the view that the axiological realm of value and morality does not exist. As Alan Pratt puts it, nihilism is the view that all values are objectively baseless.[3]
Now, either the axiological realm exists or it does not. The former proposition is axiological realism; on this view, the realm of value and morality exists either in an objective sense or in a subjective sense. The latter position is antirealism. Since either the axiological realm exists or it does not, and since ON is a theory about what things exist, the axiology of ON is either realist, antirealist, or value-neutral.
Suppose ON holds to axiological realism; then, it is either value objectivist or value subjectivist. But it is not the case that ON is either value objectivist or value subjectivist. Value objectivism requires mind-independent (i.e., non-subjective) values. Since these are not physical entities that occupy space (they cannot be measured spatially; they lack material composition; they lack weight, size, volume, etc.), nor are they arrangements of physical entities, ON is plausibly not a value objectivist worldview. Moreover, arguably, ON cannot explain consciousness. As J. P. Moreland has argued, ON lacks the conceptual resources to explain the existence of consciousness.[4] Hence, plausibly, ON is not a value subjectivist worldview, since such subjectivism requires consciousness and conscious agents. Thus, ON is inconsistent with axiological realism.
Accordingly, since ON is incompatible with realism, it seems that ON is either (a) an axiologically antirealist worldview or (b) axiologically neutral. In either case, ON lacks the explanatory resources to address sufficiently the human axiological experience — an experience the existence of which is hard to deny.
The naturalist might respond to this argument by claiming that values exist but are abstract objects and hence not part of the spatiotemporal world. This is a defensible position, but an objection comes to mind:
If, as Armstrong notes, ON is “the doctrine that reality consists of nothing but a single all-embracing spatio-temporal system,” then it seems inconsistent for the naturalist to claim that values exist as abstract objects, since abstract objects are nonspatial and atemporal entities.
[1] Papineau, D. Naturalism, Section 1.1. Stanford Encyclopedia of Philosophy. 2007. Date of Access: November 24, 2021. https://plato.stanford.edu/entries/naturalism/
[2] Armstrong, D. Naturalism, Materialism, and First Philosophy. Philosophia Vol. 8, 1978, p. 261.
[3] See Pratt, A. Nihilism. Internet Encyclopedia of Philosophy, 2020. Date of Access: November 24, 2021. https://iep.utm.edu/nihilism/
[4] Moreland, J. P. The Recalcitrant Imago Dei: Human Persons and the Failure of Naturalism. (London: SCM Press), 2009, pp. 22-23.