Cyc sets out to write down common sense

Expert systems were brittle. They knew a great deal about one narrow subject and nothing at all about the world it sat in, so that a medical program could not tell that a patient described as a 1957 Chevrolet was not a patient. Douglas Lenat's answer, begun in 1984 at the MCC research consortium in Austin, was to write down the world. Cyc, from encyclopaedia, would encode the millions of facts and rules of thumb that every adult knows and no book states: that water is wet, that people die once, that you cannot be in two places.

Lenat estimated the job at ten years and a thousand person-years. In 1994 the project became the company Cycorp, and it continued for another three decades. By the 2010s Cyc held about 25 million assertions in its own logic and was used in a handful of specialised systems.

Cyc is the most sustained attempt at the symbolic route to intelligence, and its story is the case for the other route. Large language models absorbed a rough version of common sense from text without anyone writing a rule, which is roughly what Lenat said could not work. Whether what they absorbed is knowledge in his sense is still an open argument.