Abstract. In "Mathematics is megethology," Lewis reconstructs set theory using mereology and plural quantification (MPQ). In his recontruction he assumes from the beginning that there is an infinite plurality of atoms, whose size is equivalent to that of the set theoretical universe. Since this assumption is far beyond the basic axioms of mereology, it might seem that MPQ do not play any role in order to guarantee the existence of a large infinity of objects. However, we intend to demonstrate that mereology and plural quantification are, in some ways, particularly relevant to a certain conception of the infinite. More precisely, though the principles of mereology and plural quantification do not guarantee the existence of an infinite number of objects, nevertheless, once the existence of any infinite object is admitted, they are able to assure the existence of an uncountable infinity of objects. So, if-as Lewis maintains-MPQ were parts of logic, the implausible consequence would follow that, given a countable infinity of individuals, logic would be able to guarantee an uncountable infinity of objects. §1. Introduction. In "Mathematics is megethology" Lewis (1993) reconstructs set theory using mereology and plural quantification (hereafter: MPQ). Lewis assumes from the beginning that there is an infinite plurality of atoms, whose size is equivalent to that of the set theoretical universe. So, it might seem that MPQ, though they supply a suitable language for reconstructing set theory, nevertheless they do not play any role in order to guarantee the existence of a large infinity of objects.On the contrary, we intend to demonstrate that MPQ are, in some ways, particularly relevant to a certain conception of the infinite. More precisely, though the principles of MPQ do not guarantee the existence of an infinite number of objects, nevertheless, once the existence of any infinite object is admitted, they are able to assure the existence of an uncountable infinity of objects. 1 We divide our paper into the following sections. In Section 2, we will briefly review the crucial assumptions underlying Lewis' reconstruction of set theory. In Section 3 we will construct a mereological model of the power set of any plurality of pairwise nonoverlapping individuals and show that any infinite individual has uncountably many parts. In Section 4, we will make some final remarks on the alleged innocence of MPQ, on its significance for the conception of the infinite and on the problem of impredicativity of the uncountably infinite. §2. Lewis' megethology. "Mereology," literally the "science of parts," analyzes the relation ". . . is a part of . . . ." There are different formulations of mereology depending on