In recent years there have been an increasing number of contributions to economic methodology that develop or seek to reveal ontological positions. Despite this there is no agreement about either what ontology is or how it can contribute to economics. For some ontological theorising reveals the presuppositions of economists and its role is largely descriptive. Others see ontology as primarily engaged in setting out and defending a general account of some domain of reality and suggest that such a conception can (...) help us evaluate the appropriateness of the methods economists deploy. In this paper I clarify the scope and role of such theorising in economics by considering two projects with ontological orientations, namely critical realism in economics as developed by Tony Lawson and Nancy Cartwright’s work on the nature of economic theory. I argue that there are similarities between these two projects but also differences and show that these can be better understood once we recognise that each draws on a distinct conception of the legitimate scope of ontological theorising. I use Peirce’s writings on the nature of sustainable metaphysical analysis to clarify certain aspects of the approach to ontological theorising that Lawson favours. (shrink)