I first came across Raymond Smullyan’s work — surely like many of my sort of vintage — through his wonderfully inventive and illuminating short(ish) paper “Languages in which self-reference is possible” which was reprinted in Hintikka’s 1969 The Philosophy of Mathematics (in the Oxford Readings series). Still more than worth reading, after all this time. And that paper led me to look out his First-Order Logic over forty years ago. I think it took me a while to really appreciate that classic: certainly, I kept battling on teaching first-year students Lemmon-style natural deduction for while before I was fully gripped by the loveliness of trees! I had occasion to read the first half of First-Order Logic again a few months ago, and it is such a delight.
But perhaps even more elegant, clear, readable, illuminating, getting-to-the-heart-of-things, there’s Smullyan at his very best in the three Oxford Logic Guides he published in quick succession — Gödel’s Incompleteness Theorems (1992), Recursion Theory for Metamathematics (1993), and Diagonalization and Self-Reference (1994). They give the lie to G.H. Hardy’s bitter remark that “Exposition, criticism, appreciation, is work for second-rate minds.” Smullyan’s expositions and re-organizations and novel re-appreciations and inventive drawings-out of new connections are surely the work of a first-rate mind.
And then, as a late coda, there is that other great book that Smullyan wrote with Melvin Fitting, Set Theory and the Continuum Hypothesis (1996). Those of us past the first, second, and even third flush of youth can’t but be encouraged and cheered to see Smullyan getting perhaps to the very top of his game, as far as the writing of serious logical texts is concerned, as he moves into his seventies. (The very late books like Logical Labyrinths and A Beginner’s Guide to Mathematical Logic are perhaps too uneven and quirky to really work, but still have fun and instructive episodes.)
I can’t think of a single logician whose writings I have enjoyed reading and working through more than Smullyan’s, and whose elegant lucidity I’d more like to be able to emulate. And there are few logicians that I’ve learnt as much from. So I wanted to mark Smullyan’s passing, as others have, with very warm appreciation and gratitude.
“But what about all the puzzle books? You haven’t mentioned them!” Well, I know that many others have loved them, but I very much prefer my logic served straight up: and I think it would be a sad if Smullyan is mainly remembered for them. I don’t seem to have the kind of mind that is drawn to puzzle books, to magic tricks, or Taoism: but that’s uptight Englishness for you!