During the Renaissance there was a growing interest for the use of diagrams within conceptual studies. This paper investigates the historical and philosophical foundation of this renewed use of diagrams in ontology as well as the modern relevance of this foundation. We discuss the historical and philosophical background for Jacob Lorhard’s invention of the word ‘ontology’ as well as the scientific status of ontology in the 16th and 17th century. We also consider the use of Ramean style diagrams and diagrammatic ontology in general. A modern implementation of Lorhard’s ontology is discussed and this classical ontology is compared to some modern ontologies.