Classicum

Classicum is a theoretical construct used in discussions of classification theory and ontology to denote the aggregate notion of all classes within a given system. It is distinct from individual classes in that it represents a higher‑order collective or metacategory that encompasses every class defined by the system’s taxonomy. The term blends a Latin-inspired root with a suffix that signals an abstract noun, signaling its status as a concept rather than a concrete set of individuals.

In usage, classicum is typically treated as a metaclass‑like construct rather than an ordinary class of objects. In formal description logics and ontology engineering, direct membership of an ontology’s classicum is avoided to prevent paradoxes associated with universal or all-encompassing sets; instead, it is modeled as a top‑level construct or as a properly scoped metaclass. This helps maintain clear separation between object-level classes and higher‑order classification concepts.

Examples can be helpful for illustration: in a simple taxonomy where Dog and Cat are classes, the collection of all classes in the taxonomy constitutes the classicum. Some theorists propose that the concept can aid in reasoning about cross‑hierarchy constraints, inheritance patterns, or metadata about classifications themselves, such as naming conventions or versioned schemas.

Reception to classicum is not uniform. The term remains informal in many contexts and is not part of standardized ontological practice. Critics argue that it can introduce ambiguity, and in practical ontology engineering, practitioners often prefer established notions such as metaclasses, top classes, or universal classes with explicit constraints.

See also: Metaclass, Universal class, Ontology, Taxonomy, Description logic.