- Leibniz: Body, Substance, Monad
What did Leibniz think are the true substances of the created world, and how are they related to the gross bodies and living organisms of our everyday experience? In his Leibniz: Body, Substance, Monad, Daniel Garber argues most centrally that Leibniz's views on substance and the natural world evolved over the course of his long career, and in particular that "we should isolate the middle years as a separate period in Leibniz's intellectual history . . . distinct from what precedes and what follows" (xix).
The young Leibniz, Garber argues, is best viewed as "a heretical Hobbesian," who essentially inserts immaterial minds into a Hobbes-inspired mechanistic universe (3). The result is the strange but intriguing world most familiar from Leibniz's Hypothesis physica nova and Theoria motus concreti (chapter 1; chapter 6, 225-50). Leibniz's subsequent rejection of his early efforts in physics, as well as the somewhat chaotic tenor of his early writings, lends support to Garber's suggestion that Leibniz's youthful works represent a distinct intellectual period. It is nonetheless worth noting, however, that even in his earliest writings, one finds tendencies that will persist throughout his work, including, but not limited to, a penchant for atomism of some kind or another, a willingness to at least flirt with idealism (chapter 7), and a deep-seated commitment to philosophical eclecticism and theological irenicism.
In keeping with the provocative thesis of his seminal 1985 paper, "Leibniz and the Foundations of Physics: the Middle Years," (Okruhlik and Brown, eds., The Natural Philosophy of Leibniz [Dordrecht: Reidel], 27-130), Garber argues that from roughly the end of the 1670s through much of the 1690s, "Leibniz's view of body and the physical world is grounded in a world of corporeal substances, substances understood on analogy with organisms, not minds, organic bodies transformed into substances by virtue of containing souls" (267). According to Garber, Leibniz is led to this equally strange but intriguing world primarily by two lines of thought. The first line is rooted in concerns over unity: taking unity to be a necessary condition for being, Leibniz postulates Aristotelian formal natures in order to secure unities necessary for the existence of a physical world (chapter 2). The second line is rooted in concerns over motion and force: having become more critical of mechanistic physics, including his own earlier efforts, Leibniz postulates Aristotelian formal natures in order to ground true motions and his new science of dynamics (chapters 3-4). These two lines converge with one another, as well as with various sundry metaphysical, theological, and even logical commitments (chapters 5-6) to confirm for Leibniz a picture of the world as constituted by extended, Aristotelian substances and nothing else.
And yet, according to Garber, the metaphysics of Leibniz's middle years is ultimately displaced around 1700 by a picture of the world more commonly associated with Leibniz, a world of independently unfolding, immaterial minds synchronized by a pre-established harmony (chapter 8). What was it that finally pushed Leibniz into the arms of idealism? Here as well, Garber highlights what he sees as two main paths (344-49). The first path runs once again through Leibniz's concerns with unity: pressing the demands of unity harder, Leibniz rules out substances with extended parts and commits himself to a foundation of simple substances. The second path runs through Leibniz's understanding of matter: Garber conjectures that Leibniz is led to postulate a new "sub-basement" of immaterial substances in order to provide an irreducible ground for the passive powers of his physics. These two lines of thought thus converge on a new world exhaustively constituted by unextended soul- or mind-like substances. In a suggestion that complicates the sense in which Leibniz's middle years might be viewed as a distinct period, Garber maintains that while the metaphysics of Leibniz's middle years contains the seeds of its own refutation, nonetheless Leibniz never saw his way to fully abandoning it (chapter 9 and epilogue). Leibniz died, according to Garber, still "struggling with...