One building block is placed on top of another one, an atom of sodium combines with an atom of chlorine. Do new things result in each case? Or, to put it more generally, under what conditions do various parts form a material object, i.e. a substance? Hubner addresses the problem by developing separate analyses for the composition of masses, bodies, artefacts and living organisms.

The first main line of argument develops analyses for the species named above and discusses their existence against the touchstone of classic puzzles, such as that of the ship of Theseus. The second main...