In this paper I address two important objections to the theory called '(Strong) Composition as Identity' ('CAI'): the 'wall-bricks-and-atoms problem' ('WaBrA problem'), and the claim that CAI entails mereological nihilism. I aim to argue that the best version of CAI capable of addressing both problems is the theory I will call 'Atomic Composition as Identity' ('ACAI') which consists in taking the plural quantifier to range only over proper pluralities of mereological atoms and every non-atomic entity to be identical to the (proper) plurality of atoms it fuses. I will proceed in three main steps. First, I will defend Sider's (2014) idea of weakening the comprehension principle for pluralities and I will show that (pace Calosi 2016a) it can ward off both the WaBrA problem and the threat of mereological nihilism. Second, I will argue that CAI-theorists should uphold an 'atomic comprehension principle' which, jointly with CAI, entails that there are only proper pluralities of mereological atoms. Finally, I will present a novel reading of the 'one of' relation that not only avoids the problems presented by Yi (1999aYi ( , 2014 and Calosi (2016bCalosi ( , 2018 but can also help ACAI-theorists to make sense of the idea that a composite entity is both one and many.
Keywords Mereology • Composition as Identity • Collapse • Mereological Nihilism1 '[…] perhaps the major motivation for CAI is that it implies the 'ontological innocence' of classical mereology' (Cotnoir 2014: 7). 'If Lewis's claim were that the fusion is literally identical to the cats that compose it, he would clearly be entitled to ontological innocence' (Bennett 2015: 256). '[…] the thought that a fusion is numerically identical to the things that compose it taken together […] would vindicate the intuition that such double countenancing is ultimately redundant, hence the innocence thesis' (Varzi 2014: 49). 'But why think that mereology is ontologically innocent? If composition is identity, then ontological innocence is secured' (Hawley 2014: 72).