When I came to Yale in 1966 I was the most junior of our little logic group there and Frederick Brenton Fitch was the most senior. Fitch was only one of the very unusual people I found at Yale, but he was ‘the’ logician, and I learned some very strange things from him.
Fitch was a gentleman, and a gentle man, with a deceptively understated sense of humor. He would tell us very calmly things that you’d think any logician would scream at. Our little group — Rich Thomason, Bob Stalnaker, Charles (Danny) Daniels, Bob Fogelin, Fred Fitch, and me — would meet for lunch, practically every day because Yale provided lunch free for us.
On one of the first days Fitch mentioned quietly that he was sure he would go to heaven. After all, he said, he had done something for God: he had proved his existence.
It seemed that each year he would end his seminar by proving God’s existence. On that first occasion, though, he confessed that he was still not satisfied with his proof, because by his reasoning, God turned out to be a relation.
But before I left Yale, and I asked him about it, he was satisfied. He had improved the argument and now God turned out to be a proposition. Not just any proposition, but the one true proposition that implies all true propositions — which, he said, was surely so special that it deserved to be worshipped.
Today Fitch is especially known for his Knowability Paradox. It’s called a paradox, but he offered as just a straightforward proof, that if all truths are knowable then all truths are known. Well, that does not sound believable, but logic is like that.
Self-reference was another of his topics, and we all vied to explore its paradoxes. Danny came to lunch very excited one day, brandishing a piece of paper, saying “I’ve just proved that God is not omniscient!” On the paper he had written
This proposition is not known to be true by anyone.
Could be false? No, because If it is false, then obviously it is not known to be true by anyone. So then it would be true, for that is what it says. This means that it is not false. Fine, it is not false — therefore it is true. Being true, what it says is the case, so it is not known to be true by anyone.
Conclusion: what Danny wrote down is a true proposition that is not known by anyone, not even by God! Corollary: God is not omniscient!
“Danny, Danny”, we said, “God was listening. So now he knows!”
Well, that led to more paradoxical conclusions ….
Fitch did not blanch at incredulous stares greeting his proof of the existence of God as a proposition, however silly that seemed … but sometimes I wonder … Fitch’s gently smiling rendition was perhaps not too unlike the secret smile we began to see everywhere in those sixties years …
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Note: this is a slightly revised version of what I posted in my other block on April 7, 2020 (it really seems to belong here instead)
Bas van Fraassen's Commonplace Book 
Thanks for your reply. I’ll mention just a couple of points here. First, Fitch (on pp 270-1 of that article) reproaches Hohfeld for supposedly failing to discern that the content of any duty is the negation of the content of the liberty that is the negation of the duty. Hohfeld in fact emphasized that very point. Second, throughout his article, Fitch foists upon Hohfeld a dogma from standard deontic logic whereby deontic conflicts are ruled out as a matter of logic. That is, Fitch maintained that the Hohfeldian analysis disallows any situation in which a party is under a legal duty to phi and simultaneously under a legal duty not to phi. Hohfeld himself in fact never addressed the matter of deontic conflicts, but the incorporation of that dogma into his analysis generates a medley of distortions.
To be sure, Fitch’s article is not as bad as a somewhat earlier piece by Alan Ross Anderson (“Logic, Norms, and Roles”).
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Thank you. I agree that the subject of deontic conflicts is very important and should not be set aside by fiat.
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Dear Matthew,
That is interesting, I just downloaded Fitch’s 1967 article about Hohfeld, and am surprised that you find it muddled. Could you give us a reference to the later developments that Fitch obstructed, in your view?
(If you wish you can write me through ResearchGate instead at https://www.researchgate.net/)
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Thanks for these reminiscences. Fitch is the author of one of the worst articles ever written on the Hohfeldian analysis of deontic and modal positions. The article is badly muddled, and it set back the cause of formalizing the Hohfeldian analysis for many years.
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