(Third of a three-part series.)

Leibniz published books and treatises, but much of what we know of his philosophy comes in the form of letters.  I’ve joked that he invented the calculus on the back of a cocktail napkin in the corporate lounge while his flight from Paris to Hanover was delayed, and that of course was an exaggeration for comic effect.

It wasn’t the calculus, but a dialogue on theology, and it was on a yacht from London to Rotterdam that was held fast in port by headwinds.

Leibniz by profession was a diplomat, and had been recalled from cosmopolitan Paris to dull Hanover several times (generally ignoring the orders to return while searching for academic employment), but on October 4, 1676, he left Paris, not for Hanover, but for London, where he called on various scholars and was entrusted with a letter to Spinoza for personal delivery.   A month later, he hitched a ride on the yacht of Prince Ruprecht von der Pfalz, bound for Rotterdam.

(A true philosopher: he gets someone else to pay his travel arrangements.)

From Rotterdam we know that Leibniz traveled to Amsterdam, where he met with many Spinozists, perhaps securing letters of introduction that would facilitate his meeting with Spinoza himself.   And sometime around November 18, 1676, Leibniz arrived at Spinoza’s residence in The Hague.

We’ve all played the dinner party game.  What famous person/three famous people/learned sages would you like to share a meal with/have a beer with/ask but one question?  And here, we have that.  The young diplomat and the somewhat older heretic, whom Leibniz described as:

The famous Jew Spinoza had an olive complexion and something Spanish in his face; for he was also from that country.  He was a philosopher by profession and led a private and tranquil life, passing his time polishing glass in order to make lenses for magnifying glasses and microscopes.

There are other partnerships and chance meetings in the history of philosophy, but there isn’t a meeting quite this bizarre.  It was risky for Leibniz to be associated with Spinoza.  There’s not an easy contemporary parallel, but something like a young Republican staffer dining at a known Communist sympathizer’s house during the height of McCarthyism comes close.

So what did they talk about?  We think Leibniz stayed with Spinoza from three days to ten.  Fourteen years later, Leibniz published a single page, called “That a Most Perfect Being Exists.”   In a footnote, Leibniz wrote:

I presented this argument to M. Spinosa when I was at The Hague, who thought it to be sound.  Since at first he contradicted it, I wrote it down and read this paper to him.

Spinoza never mentioned the meeting, at least not in anything of his that survived.   He died perhaps three months later, of a lung disease that was in all likelihood exacerbated by the fine ground glass that floated in the air as he shaped his lenses.

The resulting influence on Leibniz’s philosophy of Spinoza, and perhaps of this meeting, is at once obvious and hard to trace.  Leibniz in some ways defined himself in contrast to Spinoza, and one of the results of trying to avoid Spinozism is that Leibniz backs off of his commitment to the PSR, and thus from rationalism.  He ends up with a second principle, the Principle of Contradiction, which is also an independent fundamental principle.  It states (in the Monadology):

… in virtue of which we judge that which involves a contradiction to be false, and that which is opposed or contradictory to the false to be true.

The PSR is separate from this.  And this means, of course, that the PSR is not something which it would be contradictory to deny.   The PSR isn’t a conceptual truth, in other words.  But then what grounds it?  It can’t be grounded by itself.  It can’t be brute…. can it?

Thus, avoiding the consequences of Spinozism comes at a considerable cost; Leibniz must give up full-blown rationalism.

But what of the man to whose philosophy Leibniz defined himself in opposition?  While he had harsh and fiery words to say about Spinoza’s philosophy, for the man, he wrote, thirty years after their clandestine meeting:

I know that there are people of an excellent nature who would never be led by doctrines to do anything unworthy of themselves.  It can be acknowleged that Epicurus and Spinoza, for example, led entirely exemplary lives.