It has been claimed frequently that the importance of conceptual models for information systems development poses high demands on the quality of conceptual models. However, the notions “model” and “quality of conceptual models” remain vague. In this paper we illustrate how philosophical presuppositions affect the conceptualisation of “model” and “quality of conceptual models” respectively. Consequentially we argue that the analysis and critique of philosophical presuppositions should precede any theorising of the notions “model” and “quality of conceptual models”.