DESCARTES TO BERKELEY Leibniz took his doctorate at Altdorf in 1667, writing a thesis on ‘Hard Cases in Law’ He was oVered a chair, but preferred to pursue a career as a courtier and diplomat He entered the service of the Archbishop of Mainz, one of the electors of the Holy Roman Empire He dedicated his next academic publications to the archbishop: proposals for the rationalization of German law and a new method of teaching jurisprudence At the archbishop’s suggestion he republished a forgotten Wfteenth-century treatise denouncing scholastic philosophy; but he accompanied it with his own defence of Aristotle against Descartes (G I 15–27, 129–76) A Protestant in a Catholic court, he wrote a number of theological works of an ecumenical cast, concentrating on doctrines that were held in common by all Christian denominations (G IV 105–36) In 1672 Leibniz was sent on a mission to Paris, to persuade Louis XIV to lead a crusade into Egypt Diplomatically his trip was abortive, but philosophically it was fruitful He met Arnauld and Malebranche, and began a serious reading of Descartes and Gassendi He was brieXy attracted by Gassendi’s atomism and materialism, a Xirtation that he later regretted ‘When I was a youth,’ he wrote in 1716, ‘I too fell into the snare of atoms and the void, but reason brought me back’ (G VII 377) On a further diplomatic visit in the following year, this time to London, Leibniz was introduced to Boyle and Oldenburg He exhibited a model of a calculating machine to the other members of the Royal Society, who were suYciently impressed to make him a Fellow He returned to Paris and remained there until 1676, in which year he invented the inWnitesimal calculus, unaware of Newton’s earlier but as yet unpublished discoveries On his way back to Germany he visited Spinoza in Amsterdam, and studied the Ethics in manuscript, writing substantial comments But after the Ethics had been published, and Spinoza was a target of general obloquy, Leibniz played down their former intimacy From 1676 until his death Leibniz was a courtier to successive rulers of Hanover, employed in many capacities, from librarian to mining engineer He resumed the ecumenical endeavours he had started at Mainz, and began writing a book of non-sectarian Christian apologetic, for which he sought advice from Arnauld and approval from the Vatican In 1677 he wrote under an alias a book which claimed, inter alia, that the Christian states of Europe made up a single commonwealth of which the emperor was the temporal head and the pope the spiritual head 71