Abstract
Modules allow the reuse of an ontology as part of another ontology. If the ontologies do not share a common domain of discourse a simple ‘cut and paste’ approach to module reuse leads to unintended consequences, the Horatio problem. To solve this problem ISO/IEC 24707's Common Logic includes modules as a syntactic category. However, the semantics of modules is treated incongruently in ISO/IEC 24707. In this paper we propose an alternative semantics of modules, discuss their logical properties, and how they can be used in ontology development.