Cyc
knowledge base and artificial intelligence project
Cyc (pronounced SYKE) is a long-term artificial intelligence (AI) project that aims to assemble a comprehensive ontology and knowledge base that spans the basic concepts and rules about how the world works. Hoping to capture common sense knowledge, Cyc focuses on implicit knowledge. The project began in July 1984 at MCC and was developed later by the Cycorp company.
The name "Cyc" (from "encyclopedia") is a registered trademark owned by Cycorp. CycL has a publicly released specification, and dozens of HL (Heuristic Level) modules were described in Lenat and Guha's textbook, but the Cyc inference engine code and the full list of HL modules are Cycorp-proprietary.
History
The project was begun in July 1984 by Douglas Lenat at the Microelectronics and Computer Technology Corporation (MCC), a research consortium started by two United States–based corporations "to counter a then ominous Japanese effort in AI, the so-called 'fifth-generation' project." From January 1995 on, the project was under active development by Cycorp, where Douglas Lenat was the CEO.
The CycL representation language started as an extension of RLL (the Representation Language Language, developed in 1979–1980 by Lenat and his graduate student Russell Greiner while at Stanford University). In 1989, CycL had expanded in expressive power to higher-order logic (HOL).
Cyc's ontology grew to about 100,000 terms in 1994, and as of 2017, it contained about 1,500,000 terms. The Cyc knowledge base involving ontological terms was largely created by hand axiom-writing; it was at about 1 million in 1994, and as of 2017, it was at about 24.5 million.
By 2002, Cyc was described as having "consumed $60 million and 600 person-years of effort from programmers, philosophers and others—collectively known as Cyclists—who have been codifying what Lenat calls 'consensus reality' and entering it into a massive database."
In 2008, Cyc resources were mapped to many Wikipedia articles.
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Vocabulary and entity names are the principal evidence signals here, because they determine the precision of every later search. The source revision retrieved here is dated Jun 2, 2026. The linked authority identifier is Q1147294. 1 of 2 selected statements include explicit references; 1 carry qualifiers and 0 use preferred rank. The first chronological checks are 1984, 1995, 1979 and 1980.
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This entry incorporates text from “Cyc” on English Wikipedia. Contributors are listed in the page history. Text is available under the Creative Commons Attribution-ShareAlike 4.0 License. Selected authority identifiers and statements are retrieved from Wikidata under CC0; their references and qualifiers remain part of the verification path.