Cyc is the 1984 artificial-intelligence project that began building a machine-readable encyclopedia of common-sense knowledge.
The project was started by Douglas Lenat at Microelectronics and Computer Technology Corporation. Its goal was to encode facts and rules that people commonly assume without stating, such as relationships involving time, objects, intentions, and physical events. The name “Cyc” is derived from “encyclopedia.”
Cyc’s knowledge base uses formal representations rather than only ordinary prose. Its system has included assertions in a logical language known as CycL, together with collections of concepts and rules called microtheories. These structures are intended to let software draw conclusions from stored knowledge.
Cyc is different from a search engine and from a large language model. It was designed around explicit symbolic knowledge and inference. The project became a prominent example of the knowledge-engineering approach to AI, although maintaining broad common-sense knowledge proved extremely demanding.