Leibniz’s Naturalized Philosophy of Mind

Are Gottfried Wilhelm Leibniz’s metaphysics and philosophy of mind naturalistic? It may seem obvious that they are not. After all, Leibniz frequently relies on theological doctrines and argues that everything in the created world consists at bottom of immaterial substances that are beyond the scope of the natural sciences. Yet, Larry Jorgensen’s book argues the opposite—namely, that it makes perfect sense to describe Leibniz’s middle- and late-period philosophy of mind as fully naturalized. According to Jorgensen, Leibniz himself viewed his project that way and was indeed correct to do so, on a plausible conception of naturalism. Neither Leibniz’s rejection of materialism nor his reliance on theological doctrines undermines his commitment to naturalism. Quite to the contrary, his naturalism is grounded in theology.Jorgensen’s splendidly clear and wide-ranging book is the culmination of his work on Leibniz in the past decade. It incorporates and expands on many of his previously published insights about Leibniz’s theories of consciousness, perceptual distinctness, continuity, memory, and transcreation, while also branching out into new territory—for instance, Leibniz’s theories of moral identity and conceptual thought. These different strands are woven together into an extended argument for the thesis that Leibniz’s philosophy of mind is fully natural. The thesis, if true, is significant for at least two reasons: it helps us understand Leibniz’s fundamental methodological commitments and it constitutes an interesting case study of a fully natural philosophy of mind that is very different from present-day attempts at naturalization.Incidentally, the book’s title and the official statements of its thesis (3–4; 283) are somewhat misleading. After all, large portions of the book focus on topics that extend far beyond what we—and in fact Leibniz—would call ‘the mind’. The first half of the book discusses Leibniz’s naturalizing constraints generally and their application in the natural sciences (chapters 1–3), as well as Leibnizian substances generally (chapters 4–6). Only chapters 10–12 are specifically about what Leibniz calls ‘minds’—that is, rational souls. Chapters 7–9 are about the capacities that animal souls share with rational souls. I mention this not as a criticism, but rather in order to urge scholars of Leibniz’s physics and metaphysics to read this book.The book is divided into four parts, each consisting of three chapters. Part 1 investigates Leibniz’s conception of what a fully natural theory looks like. As Jorgensen acknowledges, the term ‘naturalism’ can mean many different things. Today, philosophers often use it interchangeably with ‘physicalism’, or define it in terms of what the natural sciences are able to investigate. Jorgensen is concerned with a broader understanding of the term, but one that, he convincingly argues, captures what many naturalists are after. On this understanding, a theory is naturalistic if it does not contain irresolvable mysteries—or, more precisely, if it removes sufficiently many such mysteries (2; 284). In other words, naturalized theories provide intelligible, satisfactory explanations for a sufficient number of explananda. On this conception, even explanations that invoke immaterial, nonphysical entities—for instance, Leibnizian substances—can be natural.Jorgensen derives many of his insights in the first part of the book from Leibniz’s assertion that some of his rivals’ theories—most prominently occasionalism—are nonnatural or unintelligible. One of the lessons Jorgensen draws from this is that for Leibniz, providing a natural explanation of change in a created thing means explaining the change in terms of that thing’s individual, active nature (14–15; 22). All other explanations are miraculous and hence nonnatural, which is Leibniz’s criticism of occasionalism.According to Jorgensen, Leibniz also holds that two metaphysical principles, which are grounded in God’s creative activity, are crucial for our ability to provide natural explanations. The first is the principle of continuity. It states, roughly, that there are no leaps in nature. This means, among other things, that changes must pass through all intermediate steps (47) and that between any two concepts there is an intermediate concept (50–51). The second is the principle of the best, which states that the world as a whole is as perfect as possible (51). Here, we encounter one way in which Leibniz’s naturalism is grounded in theology: the world obeys these principles—and is intelligible—because it was created by a perfectly wise and benevolent being. Thus, even though God’s activity cannot be part of naturalistic explanations (14–17), God is the reason that the world is intelligible in the first place and hence the reason that we are able to provide naturalistic explanations (30; 288–89).Given how much time Jorgensen spends on the relation between God and the created world, it is somewhat surprising that he does not discuss divine concurrence. After all, Leibniz’s endorsement of concurrentism—or the doctrine that all creaturely actions require divine cooperation—may seem to threaten his naturalism. Concurrentists claim that creatures’ powers are insufficient for explaining their actions fully; God needs to contribute to the production of these actions. This might seem to undermine naturalism, in the same way occasionalism does. In both cases, we need to know what God will do in order fully to explain what will happen. Jorgensen may have resources for solving this problem. For instance, he might argue that it is sufficient that the relevant laws are grounded in creatures, rather than God—even though we cannot fully explain the fact that creatures succeed in obeying these laws without invoking God. Still, it seems important to address this issue.Part 2 of the book examines the metaphysical basis of minds, that is, Leibniz’s fundamental ontology. We learn about Leibnizian substances, their perceptual states and forces, and the ways in which their natures explain their changing states intelligibly. Moreover, this part of the book explores Leibniz’s notion of expression and what exactly it means for the internal variety in a substance to express external things. Finally, Jorgensen also explores the notoriously difficult Leibnizian notions of perceptual distinctness and of activity and passivity.In my opinion, the discussion of activity and passivity (129–35) is not nearly as clear and persuasive as most other portions of the book. For Jorgensen, the question of whether one substance acts on another comes down to how distinctly these substances perceive each other (129). One issue with this account is that it seems unable to explain cases in which one substance acts on another in one respect, but the latter simultaneously acts on the former in a different respect. Think for instance of two children arm wrestling or pulling each other’s hair. To capture this phenomenon, we may need to interpret Leibniz as claiming that what matters for activity is not how distinctly the two substances perceive each other, but rather how distinctly they perceive the relevant change. That would also help explain the ways in which sense perception is passive. In order for my ears to receive the sound of ocean waves, the waves do not need to perceive my ears more distinctly than my ears perceive the waves (133). Rather, the waves simply need to perceive their own motion more distinctly than I do.The third part of the book is devoted to features that distinguish the most primitive substances from animal souls and human minds. Here, Jorgensen provides in-depth accounts of consciousness, memory, and desire. For each of these three notions, he provides an original interpretation of what it is and of the ways in which Leibniz’s doctrines about this notion are naturalistic. Because Leibniz holds that continuity is a necessary condition for naturalness, it would be a problem if the transition from an unconscious to a conscious state in a substance required a leap, or if there were an unbridgeable gap between creatures that are capable of conscious perception and those that are not. The same is true, mutatis mutandis, for memory and desire. Jorgensen argues that there are no such discontinuities in Leibniz’s theories of consciousness, memory, and desire when correctly interpreted.In the fourth and final part, Jorgensen finally turns to the status of rational souls and to the features that distinguish them from nonrational souls. Specifically, he addresses the big question that lingered in the background since the beginning of the book: does rationality introduce discontinuity and hence nonnaturalness into Leibniz’s system? One way in which rationality might introduce discontinuity is with respect to the origins of rational substances: it might take a genuine miracle to raise a substance to the level of rationality. Yet, Jorgensen argues that Leibniz ultimately holds that this happens without miraculous intervention. Second, rationality might introduce discontinuity through an unbridgeable gap between rational and nonrational substances—for instance, between human minds and animal souls. In order to address and dispel this second worry, Jorgensen focuses on the capacities that Leibniz often invokes when distinguishing rational minds from animal souls: the capacities to perceive one’s self and one’s moral identity, to engage in self-reflection, and to think conceptually. These capacities, he argues, do not ultimately violate naturalism either.The discussions in part 4, and particularly in the very last chapter, leave open a few pressing questions. Part 3 had discussed in enormous depth the capacities that animals share with human beings, and the question of whether these capacities violate naturalism. In part 4, however, when it comes to the capacities unique to rational beings, the discussion feels rushed. The examination of whether these capacities are compatible with the principle of continuity is relegated to the final two and a half pages of chapter 12. This is unfortunate, given the centrality of this issue to the project of the book. For instance, there is no explicit discussion of whether the consciousness exhibited in rational or abstract thought is discontinuous with other types of cognition, nor indeed of what it means to think consciously about, for instance, a number. Part 3 had bracketed that issue and concentrated instead on conscious sense perceptions (147). Part 4 does not explicitly take it up—it merely discusses self-awareness (252–57), which is a different issue. Moreover, Jorgensen concentrates almost exclusively on rational perceptions, mentioning rational appetites and freedom of the will only in passing (251). Yet, the latter seem to have at least as much potential for undermining naturalism as the special perceptual capacities of minds.These minor quibbles should not detract from how insightful and thought-provoking Jorgensen’s book is. It tackles Leibniz’s system from a fascinating new angle and is a must-read for anyone interested in Leibniz’s philosophy of mind and metaphysics. This is not the kind of book in which only one or two chapters make an original contribution and the rest serve merely as framing or background. Rather, every single chapter presents a novel and highly sophisticated solution to a thorny interpretive problem. Sadly, this also means that I was unable to summarize all of Jorgensen’s important contributions in this review—readers will have to take a look at the book for themselves

Analytic philosophy · Contemporary philosophy · Epistemology · General interest · Historical Philosophy and Science · Medieval and Classical Philosophy · Medieval Philosophy and Theology · Philosophy

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