The ontology of Gero's FBS model of designing

Recent work by Vermaas and Dorst has led to constructive criticism and conceptual clarification of Gero's FBS (Function-Behaviour-Structure) model of designing. In this paper Vermaas' and Dorst's version of the model is scrutinized, with an emphasis on its temporal aspect and ontological implications. Regarding the latter, the model is found to be in need of amendment and further refinement to ensure its clarity and logical coherence. To this end, two alternative modifications of the model are developed. These results are not claimed to be of immediate practical use to designers. Rather, they are intended to contribute to a reliable conceptual foundation for research and tool development that may aim more directly at supporting design practice.