The ‘Impartial’ Enigma: Leibniz’s Catholic Mask

Here is a question that has puzzled scholars for centuries: why would Leibniz, a Lutheran, write a book-length defence of Catholicism? This is the central mystery of his ‘Examination of the Christian Religion’ (1686), a text that feels like a jarring departure from his usual diplomatic balancing act. He claims to be a newcomer approaching the great religious schisms of Europe with fresh, unbiased eyes. Yet, as he works through the points of contention— the veneration of saints, the number of sacraments, or contested practices like communion and clerical marriage—he sides with Rome every single time.

What makes the ‘Examination’ so startling isn’t just that Leibniz defends Catholic dogmas, but that he does so with less flexibility than the Catholic negotiators of the period. While senior Catholic figures like Rojas, the Bishop of Tina, were willing to concede on issues like clerical marriage to achieve church reunion, the author of the ‘Examination’ remained uncompromising. He didn’t see these as points for negotiation, but as matters for the Pope to decide.

A clue as to Leibniz’s motivations can be found not in the rigid defence of Catholicism, but in a subtle feature of the ‘Examination’, namely that while defending Catholic positions, he repeatedly highlights variations in Catholic doctrine across history. He shows that beliefs and practices have changed over time. This is important, because if doctrine has not always been uniform, then disagreement need not imply heresy. In this way, the text may be less a defence of Catholicism than a quiet argument for tolerance.

Leibniz may have aimed this argument at a specific correspondent: Landgrave Ernst von Hessen-Rheinfels. The Landgrave was a convert to Catholicism who believed the Church’s traditions were an unvarying, monolithic block. By writing as a Catholic sympathizer, Leibniz was able to do something a Protestant never could: show the Landgrave that Catholic tradition was actually a history of change and variation. By citing obscure Church Fathers who disagreed with modern dogma, Leibniz wasn’t trying to convert; he was trying to ‘disarm’ the Landgrave’s intolerance. He was teaching him that the Church had historically tolerated a wide range of views, and perhaps should do so again. Ultimately, however, Leibniz left the ‘Examination’ unfinished and did not share it.

The ‘Examination’ remains one of the most intriguing entries in the Leibnizian archive. You can explore the full text in the new 3-volume edition of Leibniz’s Philosophical Papers. Also included are the forty marginal comments made on one of the manuscripts by Johann Daniel Gruber, a Lutheran prefect at the Royal Library in Hanover. Dating between 1745 and 1748, Gruber’s comments, which represent the earliest engagement with this seminal text, have never been published before.

— Lloyd Strickland, 27.iv.2026

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