He Taught AI the Facts of Life

Douglas Bruce Lenat, PhD ’76

December 2023

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In the 1980s, a computer program diagnosed Doug Lenat’s Chevy with measles. He loved telling the story because it illustrated a weak point in early AI: computers’ lack of common sense. Lenat dedicated 40 years of his life to changing that, trying to build an AI system that could reason like a human.

Lenat leaning on a railing overlooking sandy dunes with a penguin in the backgroundPhoto: Mary Shepherd

Douglas Bruce Lenat, PhD ’76, a former computer science professor at Stanford and an AI researcher who founded the Cyc project and Cycorp, died on August 31 of bile duct cancer. He was 72.

Lenat saw the potential for AI to democratize knowledge, with expert information available to anyone with the click of a button. “He wanted to do good in the world,” says longtime Cyc researcher Karen Pittman. 

In 1984, Lenat left Stanford to join the Microelectronics and Computer Technology Corporation as head of AI research. It was there that he founded Cyc (short for encyclopedia), an ongoing AI project to encompass the entirety of human knowledge in a single system. With a team of philosophers, linguists, and computer scientists, Lenat began to build Cyc’s knowledge base, entering fact after fact and programming the system to generalize in new, efficient ways.

“It was considered incredibly courageous, gutsy,” says Ramanathan Guha, PhD ’92, a Google Fellow and software engineer who worked on Cyc in its early years. “Lots and lots of new ideas came out of that.” Most people’s lives have been touched by techniques rooted in Cyc, he says, including reasoning at scale, representing context, and organizing hierarchies. The CIA, Goldman Sachs, and the Cleveland Clinic, among others, have asked Cyc to help them find better ways to forestall terrorism, detect insider trading, and streamline databases.

Although many recent incarnations of AI learn by consuming massive amounts of digital data, Lenat defended Cycorp’s dogged pursuit of logical reasoning and symbolic representation. In a recent paper, he made a case for incorporating a commonsense engine like Cyc into large language models, arguing that it could make AI systems like ChatGPT more trustworthy and predictable.

Every week, Lenat gathered with friends to strategize through board games or online games, with one stipulation: “He would never be the villain. He would always be a good guy,” says his wife, Mary Shepherd, who’s also an AI researcher. “If there was not a character where he could be a good person, he would not play the game, because he never, ever wanted to be a bad person. Even in a game.”

In addition to Shepherd, he is survived by his first wife, Merle Baruch; daughter, Nicole; two grandchildren; and a brother. 

Kali Shiloh is a staff writer at Stanford. Email her at kshiloh@stanford.edu.

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