Leibniz's Ripples: The Continuing Relevance of the Last Great Polymath

November 2016 marks the three hundredth anniversary of the death of whom many consider the last "universal genius," Gottfried Wilhelm Leibniz. Although there has been a flurry of scholarship on Leibniz in the last century due in no small part to the translations of some of his major logical papers and the pivotal work of Russell and Couturat, Leibniz's legacy is nevertheless difficult to evaluate. He was personally engaged with leading intellects of his time—thinkers such as Spinoza, Arnauld, Bernoulli, and de Volder—and commented on some of the most influential philosophers of the period, including Descartes, Locke, Malebranche, Berkeley, and Newton. Despite the importance of his social circle, the circumstances of his death were tragic. His funeral was poorly attended, and his reputation was tarnished due to the controversy with Newton regarding the discovery of the differential calculus. On a different level, there was also a harsh reaction in the eighteenth and nineteenth centuries against philosophical system building. And although Leibniz never had a single magnum opus on the scale of Locke's Essay Concerning Human Understanding or Hume's Treatise of Human Nature, which established their respective systems, Leibniz's writings were nevertheless very systematic in the sense that he understood that beliefs in one area of his thought would have implications for other areas. In other words, for reasons both personal and professional, Leibniz's immediate legacy was not celebrated in anywhere near the capacity to which it is appreciated today.

David Lewis once encapsulated the problem of why Leibniz's legacy is so difficult to evaluate but also gestured at why so many developments in contemporary philosophy owe a great debt to the last great polymath. Because Leibniz's vast oeuvre is a collection of over fifty thousand items, it is extremely difficult for contemporary philosophers not steeped in Leibniz scholarship to understand his importance to their work. For example, although Leibniz was the first major figure to incorporate possible worlds to track modality, he did not have fully developed possible worlds semantics like Robert Stalnaker or David Lewis. Nevertheless, even Lewis appreciated the historical precedence of Leibniz as the grandfather of possible worlds. In the preface to On the Plurality of Worlds in which Lewis famously defends modal realism, he remarks,

It may come as a surprise that this book on possible worlds also contains no discussion of the views of Leibniz. Is it that I consider him unworthy of serious attention?—Not at all. But when I read what serious historians of philosophy have to say, I am persuaded that it is no easy matter to know what his views were. It would be nice to have the right sort of talent and training to join in the work of exegesis, but it is clear to me that I do not. Anything that I might say about Leibniz would be amateurish, undeserving of others' attention, and better left unsaid.¹

Put simply, the continuing relevance of Leibniz is difficult to ascertain because Leibniz's writings are vast and sometimes inconsistent and also because current philosophy has become so hyperspecialized that it takes a rare and extraordinary philosopher to make important contributions to the contemporary landscape while at the same time understanding how those contributions would not have been possible without the thought of Leibniz. Perhaps Robert Adams is the only figure to successfully accomplish both.

One of Leibniz's most elegant analogies is that every substance is like a mirror, which reflects both the entire universe and the nature of God. Moreover, although these substances are ontologically independent of one another, they are necessarily and intimately connected to one another, such that a change in one will reflect a change in all the others. In a sense, these substances are like drops in an ocean, which cause ripples extending infinitely. As Leibniz puts it in the Theodicy, "It must be known that all things are connected in each one of the possible worlds: the universe, whatever it may be, is all of one piece, like an ocean: the least movement extends its effect there to...