 In the mereological fusion case, the issue is really just whether fusions exist at all. Those who believe in unrestricted mereological composition think that the existence of the atoms entails the existence of the fusions, and their opponents do not. The debate here is only about whether the fusions are (or would be if they existed) anything “over and above” their parts insofar as that would perhaps make them a significant ontological commitment, leading some (not Schaffer or Bennett; see above) to be suspicious of the principle of unrestricted mereological composition.