In this thesis I argue against unrestricted mereological hybridism, the view that there are absolutely no constraints on wholes having parts from many different logical or ontological categories, an exemplar of which I take to be 'mixed fusions'. These are composite entities which have parts from at least two different categories-the membered (as in classes) and the non-membered (as in individuals). As a result, mixed fusions can also be understood to represent a variety of crosscategory summation such as the abstract with the concrete, the physical with the non-physical, and the possible with the impossible, just to name a few. Proposed by David Lewis (1991) alongside his defence of classical mereology (the major theory of parthood which permits such transcategorial composites through its principle of unrestricted composition) it is my contention that mixed fusions are an under-examined consequence of indiscriminate mereological fusion which harbour a multitude of complications. In my attempt to discern their substantive character, throughout this thesis I make a case study of mixed fusions and uncover several problematic consequences which I think follow from their most plausible assessment. These include: (1) that mixed fusions' probable membership relations may lead to dubious foundational loops in the mereological Universe, or (2) otherwise that mixed fusions oblige an implausible ontological priority of the mereological Universe as a whole; (3) that mixed fusions contradict the reductive account of set theory they are proposed within, by plausibly being seen to have the same members as their class parts, and (4) that mixed fusions therefore confound a mereological thesis of Composition as Identity, which some (including Lewis) use to support classical mereology-a consequence which is potentially self-defeating; (5) that mixed fusions as sums of abstract and concrete entities both subvert Lewis's (1986) system of modal realism, while (6) also undermining less expansive theories of possible worlds; and finally, (7) that even where some of the foregoing is resisted, it remains implausible that mixed fusions are ontologically innocent, because their supposed distinction from their parts in this case ensures that they need to be counted as additional entities in one's ontology. To be clear, I do not advance a theory of mereological hybrid nihilism in the sense of denying all cases of transcategorial composition. (I only cover a few select instances of mereological hybridism via mixed fusions after all.) Rather, I deny that mereological hybridism is plausible in full generality, by demonstrating that any cases of it are at least limited by the constraints that I identify. This in turn vindicates a call for a restriction on parthood theories and 3 composition principles which allow certain types of categorially mixed entities-including restricting classical mereology with its principle of unrestricted composition. Although theories of parthood like the standard classical mereology are not ordinarily developed for ...

In this paper, I defend an unconventional mereological framework involving the doctrine of divine simplicity, to surmount a significant yet neglected dilemma resulting from that long-standing view of God as absolutely, and uniquely, simple. This framework establishes God as literally a part of everything—an “omni-part.” Although consequential for the many prominent religious traditions featuring divine simplicity, my analysis focuses on potential implications for an important formative issue in medieval Islamic philosophy. This problem of principality, with regards to metaphysical primacy and importance, derives from Ibn Sīnā’s celebrated distinction between essence and existence, and involves determining which is genuinely, objectively, real. Instead of supporting the historically dominant opposing viewpoints advancing either the principality of existence or of essence (aṣālat al-wujūd/al-māhiyya), I claim that God as omni-part aids renewed defence of the majority rejected view which upholds the combined principality of existence and essence together. Additionally, my proposal reinforces various theological desiderata including divine omnipresence and God’s necessity across possible worlds, while also supporting new perspectives on Ibn ‘Arabi’s influential notion of waḥdat al-wūjūd, understood as the absolute unity of being.