Neo-Quinean naturalised metaphysics implicitly follows the value-free ideal, excluding non-epistemic values from theory choice in the context of justification. At first glance, ethical considerations might seem wholly irrelevant to the field, apart from certain problems in social ontology and metaphysics of science. However, even some outwardly „pure“ metaphysical theories, combined with uncontroversial background assumptions, turn out to have surprising revisionary moral implications (e.g., Lewisian modal realism in Heller, 2003).

In my contribution, I advance a novel argument that ethical values ought to play a legitimate indirect role in metaphysical theory choice, and might even function as decisive tiebreakers. The proposal is motivated by the consideration I call inference risk, a counterpart to inductive risk in scientific reasoning that represents an overlooked consequence of the Quinean parity thesis and can be understood as an instance of robust moral encroachment. To illustrate how the morally grave consequences of potential false positive and false negative errors ought to inform the adjustment of the evidential threshold for the warranted acceptance of metaphysical propositions and how different first-order ethical theories bear on these decisions, I present a case study involving the personite problem (Johnston, 2016). Ultimately, I suggest that since metaphysical theories are typically underdetermined by non-empirical theoretical virtues, whose truth-conductiveness is itself contested, a socially responsible metaphysician cannot rely solely on them to guide rational theory choice.

Finally, I demonstrate that the argument avoids the problems of wishful thinking or the failure of transmission of justification (Impagnatielli, forthcoming) when ethical propositions are treated as direct counterevidence in modus tollens inferences, while still charitably explaining why naturalist metaphysicians tend to engage seriously with moral objections to their theories. I conclude by addressing objections concerning asymmetry between metaphysics and policy-oriented science, balancing of values, and the alternative of suspending judgment.

Keywords: naturalised metaphysics, theory choice, the value-free ideal, ethics, personites

References:

Barber, A. (2020). Is Metaphysics Immune to Moral Refutation? Acta Analytica, 35(4), 469–492. https://doi.org/10.1007/s12136-019-00415-y

Impagnatiello, M. O. (forthcoming). Ethics vs. Metaphysics. The Journal of Philosophy.

Johnston, M. (2016). The Personite Problem: Should Practical Reason Be Tabled? Noûs, 51(3), 617–644. https://doi.org/10.1111/nous.12159

Lloyd, A. (2025). In Defense of Robust Moral Encroachment. Social Epistemology. https://doi.org/10.1080/02691728.2025.2469186

Neto, C. (2025). The Risk of Biological Race. History and Philosophy of the Life Sciences, 47(3), article number 39. https://doi.org/10.1007/s40656-025-00684-4