Gottfried Wilhelm Leibniz

Leibniz was the son of a professor of moral philosophy at Leipzig. His father died when he was six, and he taught himself Latin and Greek in his father's library, entered the university at fifteen and took a doctorate in law at twenty. Declining a professorship, he joined the court of the Elector of Mainz and in 1672 went on a mission to Paris, where he learned mathematics from Huygens, invented the calculus independently within four years and built a calculating machine that could multiply and divide.

In 1676 he became librarian and adviser to the Duke of Hanover and held the post for forty years, charged with writing the history of the ducal house, a task never finished. He was also diplomat, engineer, historian and jurist, corresponded with over a thousand people across Europe, founded the Berlin Academy, proposed a Chinese academy of sciences to the Kangxi emperor, and was thrilled by the correspondence between the sixty-four hexagrams of the I Ching and his binary arithmetic. The priority dispute with Newton over the calculus poisoned his last years; only his secretary attended his funeral.

His philosophy is scattered through short essays, letters and one book, the Theodicy, written against Bayle. Reality consists of countless monads, unextended spiritual units of force, 'windowless', not acting on one another, yet each mirroring the whole universe from its own point of view, their agreement guaranteed by a harmony pre-established by God. God chose the best of infinitely many possible worlds to create, and evil is a necessary part of the best whole; Voltaire mocked this in Candide. He also formulated the principle of sufficient reason and the identity of indiscernibles, and dreamed of a universal symbolic language in which philosophers could say 'let us calculate'.