Leibniz entered the service of Duke Johann Friedrich of Brunswick-Lüneburg and moved to Hanover late in 1676. Court employment gave him long-term patrons and a base for wide correspondence, while also pulling him into practical work (law, politics, libraries, engineering). This setting shaped how he developed a rationalist philosophy meant to fit both science and theology.
In 1677 Leibniz gained the title of Privy Counselor of Justice, strengthening his role as a trusted legal and political adviser. The promotion helped secure the stable position that supported his long research projects and his extensive exchange of philosophical letters. His career shows how early modern philosophy was often written alongside government and court work.
Leibniz published Meditations on Knowledge, Truth, and Ideas in 1684. In it he proposes graded kinds of knowledge—such as clear vs. obscure and distinct vs. confused—and uses these distinctions as tools for judging ideas and claims. This work shows Leibniz’s rationalist goal: to make knowledge more exact by analyzing concepts and their clarity.
In 1685 Leibniz was commissioned to write a dynastic history of the House of Brunswick (the Welfs). The project required long archival research and diplomacy, and it kept him tied to court obligations for decades. It also illustrates how Leibniz’s philosophical writing had to compete with major state and family projects.
Leibniz wrote the Discourse on Metaphysics in 1686 as a compact statement of his mature metaphysics. It lays out central rationalist themes such as the role of God’s wisdom, the nature of substance, and how events can be intelligible through reasons rather than mere observation. Although not published in his lifetime, it became a key window into his system.
In February 1686 Leibniz initiated a sustained correspondence with the theologian Antoine Arnauld by sending a summary of the Discourse on Metaphysics and inviting criticism. Their exchange (1686–1690) forced Leibniz to clarify difficult doctrines like “complete concepts” (the idea that a substance’s concept includes all its true predicates). This correspondence shows Leibniz testing a rationalist system under sharp, informed objections.
In 1695 Leibniz published the New System to present his view of what substances are and how mind and body relate. A major claim is “pre-established harmony”: minds and bodies do not push each other around directly, but their states match because God set their laws in coordination from the start. This was Leibniz’s rationalist alternative to both materialism and occasionalism (the view that God intervenes at every moment to link mind and body).
Leibniz completed the New Essays on Human Understanding in 1704 as a detailed response to John Locke’s empiricist theory of knowledge. The dialogue format lets Leibniz argue that experience matters, but that the mind also contributes structures and principles that are not simply copied from the senses. He held the manuscript back and it was published only long after his death, but it became a major text in the rationalism–empiricism debate.
Leibniz published Theodicy in 1710, the only large philosophical book he released during his lifetime. It argues that belief in an all-good, all-powerful God can be consistent with the existence of evil, using ideas like “the best of all possible worlds.” The book aimed to answer skeptical arguments (especially those associated with Pierre Bayle) while keeping faith and reason in harmony.
In 1714 Leibniz wrote two short French summaries of his philosophy: Principles of Nature and Grace and the Monadology. They present a world made of “monads,” or simple substances with perception, coordinated by rational laws and divine ordering rather than by purely mechanical pushes and pulls. These late summaries were designed to make his system easier to grasp, especially for non-specialist readers at court.
From 1715 to 1716, Leibniz exchanged letters with Samuel Clarke (a defender of Newton) in a structured philosophical debate. Key issues included whether space and time are absolute “containers” or relational orderings among things, and how to understand God’s action in nature. The exchange became one of the most influential early modern arguments connecting metaphysics to the new physics.
Leibniz died on November 14, 1716, ending a career that linked court service, scientific work, and systematic metaphysics. His late summaries and public controversies helped shape later debates about rationalism, empiricism, and the foundations of science. After his death, his unpublished manuscripts and correspondence continued to fuel scholarship and influence Enlightenment and post-Enlightenment philosophy.
Gottfried Wilhelm Leibniz: rationalist metaphysics and correspondence (1676–1716)