World renowned philosopher Daniel Dennett, who championed controversial takes on consciousness and free will among other mind-bending subjects, died today at the age of 82.

(Full disclosure: This loss is personal. Dennett was our friend and a colleague of my spouse, Sean Carroll. Sean and I have many fond memories of shared meals and stimulating conversations on an enormous range of topics with Dan over the years. He was a true original and will be greatly missed.)

Stunned reactions to Dennett's unexpected passing began proliferating on social media shortly after the news broke. "Wrenching news. He's been a great friend and incredible inspiration for me throughout my career," the Santa Fe Institute's Melanie Mitchell, author of Artificial Intelligence: A Guide for Thinking Humans, wrote on X. "I will miss him enormously."

"He was a towering figure in philosophy and in particular in the philosophy of AI," roboticist Rodney Brooks (MIT, emeritus) wrote on X, bemoaning that he'd never replied to Dennett's last email from 30 days ago. "Now we have only memories of him.

A 2017 New Yorker profile described Dennett as "a cross between Darwin and Santa Claus," with "a fluffy white beard and a round belly." That jolly appearance was accompanied by an intellectual ferocity—generously embellished with his sparkling wit—as he battled such luminaries as Stephen J. Gould, John Searle, Noam Chomsky, David Chalmers, Roger Penrose, and Richard Lewontin, among others, over consciousness and evolution, free will, AI, religion, and many other topics.

Dennett's many books, while dense, nonetheless sold very well and were hugely influential, and he was a distinguished speaker in great demand. His 2003 TED talk, "The Illusion of Consciousness," garnered more than 4 million views. While he gained particular prominence as a leader of the "New Atheist" movement of the early 2000s—colorfully dubbed one of the "Four Horsemen of New Atheism" alongside Richard Dawkins, Christopher Hitchens, and Sam Harris—that was never his primary focus, merely a natural extension of his more central philosopical concerns.

David Wallace, physicist and philosopher of physics at the University of Pittsburgh, offered Ars Technica this succinct summation of Dennett's extraordinary influence:

To me, Dan Dennett exemplified what it means to do philosophy in an age of science. He once said that there was no such thing as philosophy-free science, only science that didn’t interrogate its philosophical assumptions; equally, he saw more deeply than almost anyone that the deepest traditional questions of philosophy, from free will to consciousness to metaphysics, were irreversibly transformed by modern science, most especially by natural selection.

His approach, as much as his own towering contributions, has inspired generations of philosophers, far beyond cognitive science and the philosophy of mind (his ideas have been influential in the interpretation of quantum theory, for instance). He was one of the great philosophers of the last century, and one of the very few whose work has been transformative outside academic philosophy.

"Dan Dennett was the embodiment of a natural philosopher—someone who was brilliant at the careful conceptual analysis that characterizes the best philosophy, while caring deeply about what science has to teach us about the natural world," Johns Hopkins University physicist and philosopher Sean Carroll told Ars. "At the same time, he was the model of a publicly-engaged academic, someone who wrote substantive books that anyone could read and who had a real impact on the wider world. People like that are incredibly rare and precious, and his passing is a real loss."

Born in Boston in 1942, Dennett's father was a professor of Islamic history who became a secret agent for the OSS during World War II, posing as a cultural attaché at the American Embassy in Beirut. Dennett spent his early childhood there until his father was killed in a plane crash while on a mission to Ethiopia. Dennett, his mother, and two sisters returned to Boston after that, and his family assumed he would attend Harvard just like his late father. But after graduating from Phillips Exeter Academy, Dennett opted to attend Wesleyan University instead—at least until he came across Harvard logician and philosopher W.V.O. Quine's 1963 treatise, From a Logical Point of View.

Dennett ended up transferring to Harvard to study under Quine and become a philosopher, initially intent on proving Quine wrong. By the time he was a graduate student at Oxford University, he was known among his fellow students as "the village Quinean." In his 2023 memoir, I've Been Thinking, Dennett traced his interest in applying his field to questions of science to this period. He recalled experiencing the universal sensation of one's hand falling asleep and feeling like an alien thing, rather than part of one's own body. He wondered what was going on in the body and the brain to create that sensation.

"The other philosophers thought, that’s not philosophy. I said, well, it should be," he told Tufts Now last year. "So I started learning. I didn’t even know what a neuron was back then in the early ’60s, but I soon learned. I was lucky to get in on the ground floor of cognitive neuroscience. Some of the early pioneers in that field were my heroes and mentors and friends."

Dennett's first academic position was at the University of California, Irvine, and a revised version of his doctoral thesis became his first book: 1969's Content and Consciousness. He moved to Tufts University in 1971, where he remained for the rest of his career. One of Dennett's earliest collaborators was Douglas Hofstadter, author of the bestselling Gödel, Escher, Bach: an Eternal Golden Braid, who called Dennett "a lodestar in my life" in an email [quoted with permission] to colleagues after hearing of the latter's death:

Dan was a deep thinker about what it is to be human. Quite early on, he arrived at what many would see as shocking conclusions about consciousness (essentially that it is just an emergent effect of physical interactions of tiny inanimate components), and from then on, he was a dead-set opponent of dualism (the idea that there is an ethereal nonphysical elixir called “consciousness”, over and above the physical events taking place in the enormously complex substrate of a human or animal brain, and perhaps that of a silicon network as well).  Dan thus totally rejected the notion of “qualia” (pure sensations of such things as colors, tastes, and so forth), and his arguments against the mystique of qualia were subtle but very cogent.

Dennett was a a confirmed compatibilist on the fiercely debated subject of free will, meaning that he saw no conflict between philosophical determinism and free will. "Our only notable divergence was on the question of free will, which Dan maintained exists, in some sense of 'free,' whereas I just agreed that 'will' exists, but maintained that there is no freedom in it," Hoftstadter recalled.

Johns Hopkins philosopher Jenann Ismael recalled corresponding with Dennett after her own book on free will, How Physics Makes Us Free, was published in 2016.  She had not yet met Dennett, but his work was naturally a significant influence, even though her book was largely critical of his stance on the subject. Ismael opened her book by discussing Dennett's fictional short story, "Where Am I?", calling it "the best of piece of philosophical fiction ever written." (Check out this short film based on the story, starring Dennett himself uttering such immortal lines as, "They made a sparkling new vat for my brain.")

Dennett read her book and emailed Ismael with a few notes—not about how he felt she'd misrepresented his views (which he deemed of "no matter") but correcting her mistakes about the plot of his short story. "It turns out I got the story wrong," Ismael told Ars.  "I'd read it so long ago, I just embellished it in my head and embarrassingly never realized. Where I criticized him in my book, he wasn't as keen to correct me as he was excited to talk about the ideas."

She found him to be filled with infectious warmth. "It was true that he could suck the air out of a room when he entered and even sitting at a round dinner table, he somehow became the center of it, he took possession of the discussion," said Ismael. "But he also paid close attention to people, read voraciously, listened to and heard what others were saying, taking what he could and disseminating what he learned. He had immense curiosity and he wanted to share everything that he learned or liked."

In his later years, Dennett wasn't shy about sounding the alarm regarding AI, even writing an article for The Atlantic last year on the topic about the dangers ahead, particularly with the advent of large language models like ChatGPT.  "The most pressing problem is not that they’re going to take our jobs, not that they’re going to change warfare, but that they’re going to destroy human trust," he told Tufts Now. "They’re going to move us into a world where you can’t tell truth from falsehood. You don’t know who to trust. Trust turns out to be one of the most important features of civilization, and we are now at great risk of destroying the links of trust that have made civilization possible."

Dennett was not one to traffic in false modesty over his many accomplishments and always evinced a strong degree of self-confidence, fondly recounting in his memoir of the time fellow philosopher Don Ross wryly observed, "Dan believes modesty is a virtue to be reserved for special occasions."

His myriad interests weren't limited to the academic. Dennett loved art, music, sailing, pottery, trout fishing, windsurfing, ran his own cider press, and made his own Calvados on a Prohibition-era still. He could call a square dance, whittle a wooden walking stick, and was fond of pondering knotty philosophical questions while driving his tractor on his 200-acre farm in Blue Hill, north of Boston, which he bought in the 1970s. (He sold the farm around 2014.)

"Dan was a bon vivant, a very zesty fellow, who loved travel and hobnobbing with brilliance wherever he could find it," Hoftstadter wrote in his tribute.  "In his later years, as he grew a little teetery, he proudly carried a wooden cane with him all around the world, and into it he chiseled words and images that represented the many places he visited and gave lectures at. Dan Dennett was a mensch, and his ideas on so many subjects will leave a lasting impact on the world, and his human presence has had a profound impact on those of us who were lucky enough to know him well and to count him as a friend."

Ismael recalled him sending her YouTube videos of "swing dancing and silly outfits" during the pandemic, his emails littered with colorful emojis. He was "a strange man, who didn't take himself as seriously as you might think," she said. "I really loved him, loved his spirit, his generosity, the expansiveness of his thinking, his delight in ideas, and his great good cheer. Philosophically, I think he had true greatness. It seems impossible he is gone."