Two notions of fusion and the landscape of extensionality

There are two main ways in which the notion of mereological fusion is usually defined in the current literature in mereology which have been labelled ‘Leśniewski fusion’ and ‘Goodman fusion’. It is well-known that, with Minimal Mereology as the background theory, every Leśniewski fusion also qualifies as a Goodman fusion. However, the converse does not hold unless stronger mereological principles are assumed. In this paper I will discuss how the gap between the two notions can be filled, focussing in particular on two specific sets of principles that appear to be of particular philosophical interest. The first way to make the two notions equivalent can be used to shed some interesting light on the kind of intuition both notions seem to articulate. The second shows the importance of a little-known mereological principle which I will call ‘Mild Supplementation’. As I will show, the mereology obtained by adding Mild Supplementation to Minimal Mereology occupies an interesting position in the landscape of theories that are stronger than Minimal Mereology but weaker than what Achille Varzi and Roberto Casati have labelled ‘Extensional Mereology’.

The Bundle Theory Approach to Relational Quantum Mechanics

The present essay provides a new metaphysical interpretation of Relational Quantum Mechanics (RQM) in terms of mereological bundle theory. The essential idea is to claim that a physical system in RQM can be defined as a mereological fusion of properties whose values may vary for different observers. Abandoning the Aristotelian tradition centered on the notion of substance, I claim that RQM embraces an ontology of properties that finds its roots in the heritage of David Hume. To this regard, defining what kind of concrete physical objects populate the world according to RQM, I argue that this theoretical framework can be made compatible with (i) a property-oriented ontology, in which the notion of object can be easily defined, and (ii) moderate structural realism, a philosophical position where relations and relata are both fundamental. Finally, I conclude that under this reading relational quantum mechanics should be included among the full-fledged realist interpretations of quantum theory.

Is Sider still a perdurantist?

In Writing the Book of the World (2011) Theodore Sider claims that on the fundamental level of reality there are no objects composed of parts, which makes his view a version of mereological nihilism. However, in his previous book entitled Four-Dimensionalism (2001), Sider endorses mereological universalism, the thesis that every class of objects has a mereological fusion, i.e. that there exists an additional object containing those objects as parts, which plays a crucial role in his argument from vagueness in favour of perdurantism, that is the thesis of the existence of temporal parts of material objects. In this paper I will investigate whether Sider can still be a perdurantist in spite of his latest commitment to mereological nihilism.