Leibniz, Gottfried Wilhelm (1646–1716)
Authors: Garber Daniel 
Published: September 2018

Leibniz was one of the central figures of seventeenth-century philosophy, indeed, one of the central intellectual figures of his age. Born and educated in Germany, he travelled to Paris in 1672 and quickly entered into its lively intellectual and scientific life, acquainting himself with the most advanced ideas then in circulation. It was there that he invented the infinitesimal calculus, and laid the foundations for the philosophical and scientific programmes that were to occupy him for the rest of his life. He returned to Germany in 1676, entering the service of the House of Hanover where, except for brief absences, he remained until his death. There, along with his court duties, he had time for a wide variety of intellectual activities that eventually gained him an international reputation.
Leibniz’s philosophy, particularly his metaphysics, can appear otherworldly and complex. But there are a few simple themes and basic commitments that run through his thought. At root is his philosophical optimism, the commitment that this is the best of all possible worlds, freely created by a rational God who always chooses the best for a good reason. This best of all possible worlds, Leibniz held, is ‘the one which is at the same time the simplest in hypotheses and the richest in phenomena’ (Discourse on Metaphysics §6). For this reason, the world must be governed by a variety of general principles to which Leibniz appealed in his philosophy: there must be a sufficient reason for everything in the world; there are no jumps in nature; there must be exactly the same power in the full cause as there is in the complete effect, among many others. While such principles do not deductively determine the rest of Leibniz’s philosophy, they do play a major role in shaping it; they constitute a kind of lens through which he viewed the major philosophical issues of his age.
One such issue concerns the ultimate make-up of the world. Like many of his contemporaries, Leibniz adopted a mechanistic view, according to which everything in the physical world is explicable in terms of the size, shape and motion of the tiny bodies that make up the grosser bodies of experience. But he rejected the idea that this could be the ultimate explanation for things. Behind the mechanistic world of inanimate bodies in motion, Leibniz saw a world of living things and souls – active, genuinely individual, genuinely different from one another, the true atoms of nature, the true reality – which he eventually called monads. At the deepest level, Leibniz’s world was made up of an infinity of mind-like entities, each with its own perceptions that change from moment to moment according to an internal programme by way of the faculty of appetition, all in harmony with one another so that they all reflect the same world. While the world of physics is mechanistic, it is merely phenomenal, the confused appearance of a deeper reality. A consequence of this was Leibniz’s famous doctrine of pre-established harmony. In contrast to Descartes, for whom mind and body interact, and in contrast to the occasionalists, for whom God is the true cause who brings about motion in the body on the occasion of a volition and a sensation in the mind on the occasion of a stimulation of the appropriate nerves in the body, for Leibniz God created the mind (a single monad) and the body (itself a collection of monads) in perfect harmony with one another so that their mental and physical states would always correspond in the appropriate way.
A second set of metaphysical issues of central concern to Leibniz involves the interlocking questions of necessity, contingency and freedom. In response to contemporaries such as Hobbes and Spinoza, Leibniz tried to find room for contingency and freedom in his world. He argued that even though God is, in a sense, constrained to choose the best, he does so freely. Consequently, the world he created, the best of all possible worlds, exists contingently, and at least some features of it are contingent, those whose contraries are not in themselves impossible. So for example, 2 + 3 = 5, true in every possible world, is necessary, while ‘Adam sins’, whose contrary is not impossible, is contingent. But over and above contingency and divine freedom, Leibniz also wanted to make room for human freedom. According to Leibniz, when God created Adam as a part of this best of all possible worlds, he knew that Adam would sin; it is part of the concept of Adam that he sins, part of his internal ‘programme’ that he will eat the apple, and part of the internal ‘programmes’ of the monads that make up his body that he will actually eat the apple. But, Leibniz argued, what God builds in is that Adam freely chose to sin. God builds into the world the reasons that incline Adam’s will without necessitating it, correctly predicting what Adam will do, and building the rest of the world around the consequences of Adam’s free actions.
Important as they are, these two concerns constitute only a small portion of Leibniz’s thought, even within the domain of philosophy. In psychology, he introduced a distinction between conscious and unconscious perceptions and tried to understand the way in which unconscious perceptions (‘petites perceptions’) in part determine conscious perceptions (‘apperceptions’). In epistemology, he is important for his sophisticated version of the innatist hypothesis, and for appreciating the role that a mathematical theory of probability can play in understanding the world. In logic, Leibniz advanced programmes for a new formal logic more powerful than Aristotle’s, and for a universal language. In ethics and political thought, he contributed to the seventeenth-century natural law tradition. In natural philosophy, he emphasized the importance of the notion of force and advanced the broadly Cartesian programme of a physics grounded in conservation laws. Outside philosophy he is well known for his work on the calculus. Though he co-discovered it with Newton, it is his notation that is still used, and his version probably had the greater influence in his day. But he was a major contributor to many other fields, including geology, natural history, linguistics and European history. Though he left no real school of followers, he deeply influenced philosophy after his death, particularly in eighteenth-century Germany.