The indispensability argument (ia) comes in many different versions that all reduce to a general valid schema. Providing a sound ia amounts to providing a full interpretation of the schema according to which all its premises are true. Hence, arguing whether ia is sound results in wondering whether the schema admits such an interpretation. We discuss in full details all the parameters on which the specification of the general schema may depend. In doing this, we consider how different versions of ia can be obtained, also through different specifications of the notion of indispensability. We then distinguish between schematic and genuine ia, andargue that no genuine (non-vacuously and non-circularly) sound ia is available or easily forthcoming. We then submit that this holds also in the particularly relevant case in which indispensability is conceived as explanatory indispensability. * Many thanks to the audience of the Indispensability and Explanation workshop held at IHPST in Paris in November 19-20, 2012, where this paper was first presented. We are particularly grateful to Henri Galinon for his useful rejoinder at the conference and for subsequent discussion. The authors would like to thank the projects which financially supported their research for this article. Marco Panza wishes to thank the ANR-DFG Project Mathematical objectivity by representation. Andrea Sereni wishes to thank the Italian National Project PRIN 2010 Realism and Objectivity. 1 3 Something akin to a form of indispensability argument for abstract entities in semantics can be traced back to [Church, 1951]. Thanks to an anonymous reviewer for pointing us to Church's classic paper in this connection. As noticed by [Psillos, 1999], pp.10-11, the indispensability of the use of theoretical terms in the formulation of "efficacious" systems of laws is claimed in [Carnap, 1939], p.64. 4 Thanks to Maria Paola Sforza Fogliani for bringing this to our attention.