Because the Cyc KB contains hundreds of thousands of assertions (aka "rules"), many approaches commonly taken by other inference engines (such as frame-based expert system shells, RETE match, Prolog, etc.) just don't scale up to KBs of this size. As a result, the Cyc team has been forced to develop other techniques.

Cyc also includes several special-purpose inferencing modules for handling a few specific classes of inference. One such module handles reasoning concerning collection membership/disjointness. Others handle equality reasoning, temporal reasoning, and mathematical reasoning.

CycL^TM: the Cyc representation language

CycL, the Cyc representation language, is a large and extraordinarily flexible knowledge representation language. It is essentially an augmentation of first-order predicate calculus (FOPC), with extensions to handle equality, default reasoning, skolemization, and some second-order features. (For example, quantification over predicates is allowed in some circumstances, and complete assertions can appear as intensional components of other assertions.) CycL uses a form of circumscription, includes the unique names assumption, and can make use of the closed world assumption where appropriate.

For more information, see the detailed description of CycL language features.