Alastair Wilson, Birmingham, gives a talk for the Power Structuralism in Ancient Ontologies series Abstract: Jonathan Schaffer has recently defended the doctrine of quidditism against an epistemological challenge, claiming that the challenge amounts to nothing more than ‘external-world scepticism writ small’. I disagree with this assessment. The cases are significantly disanalogous, and quiddistic scepticism is much harder to avoid than external-world scepticism. Ultimately, the epistemological challenge is indecisive: quidditists can live with the sceptical conclusion. But there is a stronger anti-quidditist argument in the vicinity. Following John Hawthorne, I show how the epistemological challenge can be reformulated as an argument from theoretical parsimony. I argue that whether the parsimony argument is decisive depends on wider issues in the metaphysics of modality: different accounts of modality yield different verdicts about parsimony. The upshot is that we cannot expect to make progress in the quidditism debate while remaining neutral on the nature of modality.