Atomicity is the thesis that everything is ultimately composed of atoms, entities that lack proper parts. Atomicity is standardly defined as “for every x there is a y such that y is an atom and y is a part of x”, i.e. everything has an atom as a part. But does this definition really capture atomicity? In a recent paper in Philosophical Studies, “How do you say ‘everything is ultimately composed of atoms’?”, Anthony Shiver (University of Georgia) presents a countermodel to this definition. According to Shiver, the model he presents satisfies the definition, since every object in the model has an atom as a part. Yet it is not true that everything is ultimately composed of atoms, since every composite object in the model has also a composite part. Shiver proceeds to present his own definition of atomicity—“Everything is a part of a sum of atoms”—that is not subject to the same problem. Anthony Shiver, you’re it!