In 17th-century France, there was an ongoing, major religious and political dispute between the Jesuits and the Jansenists.

‘Jesuit’ is the popular name for members of the Society of Jesus, which was founded in 1539 by the Spanish soldier, St. Ignatius of Loyola (1491–1556). The Society was set up on militaristic rather than conventional monastic lines, and its head is known as the ‘General’ of the Society. The original intention was a crusade against the infidel in the Holy Land; but it soon turned into a crusade against the Reformation, which had become a serious threat to Catholicism by the time of the Augsburg Confession (1530). Loyola’s great work, the Spiritual Exercises, was completed in about 1548.

The Jesuits laid great stress on the intellect, and they have always been renowned for their scholarship and philosophical skill. On the other hand, they were often criticised for moral laxity, and for their ability to find a justification for any immoral act (hence the expression ‘Jesuitical’. During Arnauld’s time, the Sorbonne (the Theology Faculty of the University of Paris) was dominated by Jesuits.

The Jansenists were not a religious order as such, but a movement which adhered to the principles of Cornelius Jansen (1585–1638), Bishop of Ypres. His views were expressed in his posthumously published Augustine (1640). As the title implies, he took his inspiration from the Platonist St. Augustine, as opposed to the Aristotelian St. Thomas Aquinas. In many respects his theology was quite close to that of the Calvinists, including a belief in predestination, and in the inability of the natural human will to attain goodness. He attacked scholastic language and logic as incapable of embodying religious mystery, and as useless for practical reasoning. Although he held that true religion was possible only through the Catholic Church, his emphasis was on the personal and individual relation between the human soul and its maker.

One of Jansen’s most vehement supporters was a Paris lawyer, called Antoine Arnauld (1597–1619). The Antoine Arnauld who Leibniz corresponded with was his twentieth child, and he became known by his contemporaries as the ‘great’ Arnauld, to distinguish him from his father. Antoine Jr. was born in 1612. He studied theology at the Sorbonne, but later came under the influence both of Jansenism and Cartesianism. In 1643, he published a book called On Frequent Communion, which did more than any previous work to make Jansenist ideas widely known and understood. However, it caused a scandal, and Arnauld was forced to live in seclusion for most of the rest of his life.

He spent many years at the convent of Port Royal, near Paris. Its abbess was his sister Angélique (1591–1661), who had reformed it, and turned it into a stronghold of Jansenism. She established a school for the children of Jansenists (one of the pupils being the poet Jean Racine). She was succeeded by her niece, also called Angélique (1624–1684). Among Arnauld’s collaborators at Port Royal were Blaise Pascal (1623–1662), and Pierre Nicole (1625–1695).

In 1655, Arnauld published an attack on Jesuit casuistry, which led to his condemnation as a heretic, and the stripping of his degree by the theologians of the Sorbonne. Pascal tried to save him with his series of vicious and beautifully written diatribes against the Jesuits, the pseudonymous Provincial Letters (1656–1657). Some years later, Arnauld received the favour of Louis XIV, and was able to emerge from his seclusion for a while. But the persecution returned, and Arnauld had to flee France in 1678, when a warrant for his arrest was issued. He finally settled in Brussels, where he died in 1694.

Arnauld was a very prolific writer on theology, philosophy, logic, grammar, and mathematics. The first collected edition of his works (1775–1783) amounted to 45 volumes. The most famous of his writings, and the one with the longest-lasting influence, was produced in collaboration with Nicole. It is usually known as the ‘Port Royal Logic’, but its actual title was Logic, or the Art of Thinking, first published (anonymously) in 1662.

In 1679, Leibniz made the acquaintance of Landgrave (roughly = Count) Ernst von Hessen-Rheinfels, who had been using the Hanover library. Ernst was a convert from Protestantism to Catholicism, and a friend of Arnauld. He also shared with Leibniz and the Duke an ambition to achieve the re-unification of the Churches. Ernst and Leibniz corresponded regularly about religion, philosophy, and other matters.

1686 is usually seen as a pivotal point in the development of Leibniz’s philosophy, since it was when he first tried to put it down on paper as a systematic whole. I personally don’t see much of a discontinuity with what went before; but it is certainly a period when he focussed his attention rather more than usual in philosophy as such. The paper he produced (in French) is known as the Discourse on Metaphysics, though there is no title on the manuscript. It may have circulated in MS form, but it was not printed until 1846.

Leibniz’s motivation in writing was, at least partly, his view that he had discovered a new metaphysical system which could help reunite the Churches if it were generally accepted. In particular, he believed he could give an account of transubstantiation which could be acceptable to both sides (this comes out particularly clearly in his much later correspondence with Des Bosses).

Through the mediation of Ernst, Leibniz sent Arnauld the paragraph headings of the Discourse, but not the whole text. There then followed a lengthy correspondence between Leibniz and Arnauld, which continued at least until 1690. Leibniz was still quite young (39) and relatively unknown, whereas Arnauld was 73, and very much the Grand Old Man of French philosophy in the post-Cartesian era.

I have translated from Gerhardt, Philosophischen Schriften, Vol. 2. The 3-way correspondence (all in French) between Leibniz, Arnauld, and Ernst von Hessen-Rheinfels occupies pp.11–138. There are lengthy extracts from it in Francks and Woolhouse (pp.94–138).

Here I have included just one extract from Leibniz’s letter of 9.10.1687. In this extract, Leibniz clearly states his phenomenalist position: only true unities (perceivers) are real, and material things are not unities. Here the argument turns on the rather Platonic thesis that matter can never be precisely determinate. For a thing to be real, it must be exactly what it is — but material things are never exactly anything.

Go to the Index to Leibniz’s correspondence with Arnauld