The Structural Cost of Plausibility: McDaniel, Lewis, and the Modal Dilemma

 

The Structural Cost of Plausibility: McDaniel, Lewis, and the Modal Dilemma

The history of modal metaphysics may be understood as an extended attempt to reconcile two concepts first articulated by Aristotle: dynamis (δύнаμις), the capacity for being otherwise, and energeia (ἐνέργεια), actuality or realized being. Every theory of modality must answer a deceptively simple question: what is the ontological status of that which is possible but not actual? Contemporary modal realism represents perhaps the most ambitious effort to answer this. Yet the debate between David Lewis and Kris McDaniel reveals that the central problem is not merely whether possible worlds exist, but what kind of existence possibility itself requires.

David Lewis famously proposed that possible worlds are concrete, spatiotemporally isolated totalities—a plurality of realities no less real than our own. The explanatory power of this system is extraordinary. Modality, counterfactuals, essentialism, and modal logic are unified within a single ontological framework. Yet many philosophers have regarded Lewis’s ontology as an instance of what the scholastics might have called nimia multiplicatio entium—an excessive multiplication of entities. Kris McDaniel’s revisionary modal realism emerges from precisely this concern. By replacing strict modal isolation with overlapping worlds structured by tropes and relations, McDaniel seeks to preserve realism while reducing ontological extravagance.

I argue, however, that McDaniel’s achievement is more ambiguous than it first appears. His revisions succeed in making modal realism more intuitively plausible, but only by transferring explanatory burdens from ontology to structure. Lewis purchases systematic unity at the cost of ontological abundance; McDaniel purchases ontological restraint at the cost of theoretical stability. The resulting dispute is not fundamentally about possible worlds; rather, it concerns two competing visions of metaphysical explanation itself: one privileging systematic coherence (logos), the other privileging phenomenological plausibility (phainomena).

Lewis’s modal realism is not merely an extravagant ontology but a profoundly systematic metaphysical vision. Like Parmenides, Lewis seeks explanatory unity through ontological consistency. Every world is of the same ontological type, and actuality functions indexically, much like "here" or "now." This achieves what Aristotle called scientia propter quid—knowledge through explanatory principles. The remarkable feature of Lewis's system is that its most controversial elements—modal isolation, world-bound individuals, and counterpart theory—form an integrated architecture exhibiting what Leibniz might have called a harmonia metaphysica (Leibniz 34). Yet the very coherence of Lewis's system generates its greatest liability: to explain possibility, Lewis asks us to accept an infinite plurality of concrete universes.

McDaniel’s program begins from a recognition that many objections to Lewis target specific theoretical commitments rather than realism itself. McDaniel rejects the doctrine of world-bound individuals, permitting overlap between worlds. A single object may literally exist in multiple worlds, restoring what Aristotle might have recognized as the unity of a substance (ousia, οὐσία) across different possibilities (McDaniel 134). This move restores intuitive plausibility, yet it introduces the classic problem of individuation. If McDaniel employs tropes—particularized properties—to build these worlds, he inherits the principium individuationis (principle of individuation) that has plagued metaphysics since the medievals. If two numerically distinct apples share an identical shade of red, what grounds the distinctness of their redness tropes? Without a clear archē tēs diaireseōs (principle of division), McDaniel’s tropes risk becoming primitively distinct, replacing Lewis’s ontological inflation with arbitrary structural assertion.

Furthermore, McDaniel’s rejection of Lewisian indexical actuality in favor of absolute actuality introduces a problematic "brute fact" into his system. For Lewis, actuality is not a privileged status; for McDaniel, one world is genuinely actual. This aligns with common sense, but it threatens the principium rationis sufficientis (principle of sufficient reason)—nihil est sine ratione (nothing is without a reason). Without a structural account of why one world is privileged, actuality becomes a metaphysical designation lacking explanatory grounding. McDaniel also inherits the burden of explaining how overlapping objects can exist across worlds without creating cross-world causal leakage, a problem Lewis avoids entirely through his strict causal isolation.

Ultimately, the choice between Lewis and McDaniel rests on the cost of intelligibility. Lewis offers a theory that is ontologically extravagant but architecturally unified; McDaniel offers a theory that is considerably more plausible but structurally unstable. The disagreement forces us to return to the ancient challenge: how can possibility possess reality without multiplying it beyond necessity? Lewis and McDaniel represent two sophisticated contemporary attempts to answer this. Their disagreement reveals that the true challenge of modal metaphysics is not determining what is possible, but determining what sort of reality possibility requires. Whether one prioritizes the Parmenidean demand for systematic unity or the Aristotelian sensitivity to the complexity of experience, the central task remains: to ground possibility in a way that respects the limits of metaphysical explanation.

Works Cited

Armstrong, D. M. A World of States of Affairs. Cambridge UP, 1997.

Leibniz, Gottfried Wilhelm. Monadology. 1714. Translated by Robert Latta, Oxford UP, 1898.

Lewis, David. On the Plurality of Worlds. Blackwell, 1986.

McDaniel, Kris. "Modal Realisms." Philosophical Studies, vol. 125, no. 2, 2005, pp. 131-152.