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In philosophy, mereological nihilism (also called compositional nihilism) is the metaphysical thesis that there are no objects with proper parts. Equivalently, mereological nihilism says that mereological simples, or objects without any proper parts, are the only material objects that exist.[dubious ]
Our everyday perceptual experience suggests that we are surrounded by macrophysical objects that have other, smaller objects as their proper parts. For example, there seem to be such objects as tables, which appear to be composed of various other objects, such as the table-legs, a flat surface, and perhaps the nails or bolts holding those pieces together. Those latter objects, in turn, appear to be composed of still smaller objects. And so on. Indeed, every putative material object our perceptual faculties are capable of representing appear to be composed of smaller parts.
Mereological nihilists claim that there are no composite material objects. According to mereological nihilism, there are only fundamental physical simples arranged in various spatial patterns. For example, the mereological nihilist claims that, despite appearances to the contrary, there really are no tables. There are only fundamental physical simples spatially arranged and causally interrelated in such a way as to jointly cause perceptual faculties like ours to have table-like perceptual experiences. Nihilists often abbreviate claims like this one as follows: there are fundamental physical simples arranged table-wise.
This seems to devolve into an error theory. If there are no composite objects, how can we make sense of our ordinary understanding of reality which accepts the existence of composite objects? Are we all deceived? Ted Sider argued in a 2013 article that we should think of composition as arrangement. According to Sider, when we say "there is a table", we mean there are mereological simples arranged table-wise.
Mereology (from the Greek μερος, 'part') is the theory of parthood relations: of the relations of part to whole and the relations of part to part within a whole. Its roots can be traced back to the early days of philosophy, beginning with the Presocratic atomists and continuing throughout the writings of Plato (especially the Parmenides and the Theaetetus), Aristotle (especially the Metaphysics, but also the Physics, the Topics, and De partibus animalium), and Boethius (especially In Ciceronis Topica).
As can be seen from Varzi's passage, classical mereology depends on the idea that there are metaphysical relations that connect part(s) to whole. Mereological nihilists maintain that such relations between part and whole do not exist.
Nihilists typically claim that our senses give us the (false) impression that there are composite material objects, and then attempt to explain why nonetheless our thought and talk about such objects is 'close enough' to the truth to be innocuous and reasonable in most conversational contexts. Sider's linguistic revision that reformulates the existence of composite objects as merely the existence of arrangements of mereological simples is an example of this. Tallant (2013) has argued against this maneuver. Tallant has argued that mereological nihilism is committed to answering the following question: when is it that a group of mereological simples is arranged in a particular way? What relations must maintain among a group of mereological simples such that they are arranged table-wise? It seems the nihilist can determine when a group of objects compose another object: for them, never. But the nihilist, if he is committed to Sider's view, is committed to answering how mereological simples can be arranged in particular ways.
The objection that can be raised against nihilism is that it seems to posit the existence of far fewer objects than we typically think exist. The nihilist's ontology has been criticized for being too sparse, as it only includes mereological simples, and denies the existence of composite objects that we intuitively take to exist, like tables, planets, and animals. Another challenge that nihilists face arises when composition is examined in the context of contemporary physics. According to findings in quantum physics, there are multiple kinds of decomposition in different physical contexts. For example, there is no single decomposition of light; light can be said to be either composed of particles or waves depending on the context. This empirical perspective poses a problem for nihilism because it does not seem like all material objects perfectly decompose to mereological simples.[dubious ] In addition, some philosophers have speculated that there may not be a "bottom level" of reality. Atoms used to be understood as the most fundamental material objects, but were later discovered to be composed of subatomic particles and quarks. It is then possible that the most fundamental entities of current physics can actually be decomposed further than what is currently considered their base form, and their parts can be further decomposed.[dubious ] If matter is infinitely decomposable in this respect, then mereological simples do not exist as an absolute entity. This poses a conflict with an initial assumption within Mereological Nihilism according to the belief that only mereological simples exist.
Partial vs. pure nihilism
Philosophers in favor of something close to pure mereological nihilism include Peter Unger, Cian Dorr, and Ross Cameron. There are a few philosophers who argue for what could be considered a partial nihilism, or what has been called quasi-nihilism, which is the position that only objects of a certain kind have parts. One such position is organicism: the view that living beings exist, but there are no other objects with parts, and all other objects that we believe to be composite—chairs, planets, etc.—therefore do not exist. Rather, other than living beings, which are composites (objects that have parts), there are only true atoms, or basic building blocks (which they call simples). Organicist philosophers include Trenton Merricks and Peter van Inwagen.
Van Inwagen's view
Peter Van Inwagen maintains that all material objects are mereological simples with the exception of biological life such that the only composite objects are living things. Van Inwagen's view can be formulated like this: "Necessarily, for any non-overlapping xs, there is an object composed of the xs iff either (i) the activities of the xs constitute a life or (ii) there is only one of the xs."In other words, Van Inwagen contends that mereological atoms form a composite object when they engage in a sort of special, complex activity which amounts to a life. 
One reason why Van Inwagen's solution to the Special Composition Question is so attractive is that it allows us to account a conscious subject as a composite object. Nihilists have to maintain that the subject of a single consciousness is somehow the product of many discrete mereological atoms. Van Inwagen's argument against nihilism can be characterized as such:
- I exist
- I am not a mereological simple
- At least one object exists that is not a mereological simple
- So, nihilism is false
In addition to allowing for the existence of trees, cats, and human beings, Van Inwagen's view is attractive because it inherits nihilism's elegant solutions to traditional problems in mereology like the Ship of Theseus and the problem of the many.
One objection that can be offered against Van Inwagen's view is the vagueness of the category of life and the ambiguity of when something gets "caught up" in a life. For example, if a cat takes a breath and inhales a carbon atom, it is unclear at what point that atom becomes officially incorporated into the cat's body.
- Buddhist atomism
- Elementary particles
- Mereological essentialism
- Metaphysical nihilism
- Peter van Inwagen
- Trenton Merricks
- Sider, Theodore (2013). Against Parthood. Oxford Studies in Metaphysics 8:237–293.
- Mereology, Stanford Encyclopedia of Philosophy
- Sider, Theodore (2013). Against Parthood. Oxford Studies in Metaphysics 8:237–293.
- Tallant, Jonathan (2013). Against mereological nihilism. Synthese 191 (7):1511-1527.
- Healy, Richard (2013). "Physical Composition". Studies in History and Philosophy of Modern Physics. 44: 48–62.
- Ney, Alyssa. Metaphysics: An Introduction. Routledge. pp. 111–112.
- Merricks, Trenton (2001). Objects and Persons. New York: Oxford University Press.
- van Inwagen, Peter (1990). Material Beings. Ithaca: Cornell University Press.
- Ned Markosian. Sider; Hawthorne; Zimmerman (eds.). Contemporary Debates in Metaphysics. pp. 341–363. CS1 maint: discouraged parameter (link)
- ney. Metaphysics: An Introduction. Routledge. ISBN 978-0415640756.
- Markosian. "Restricted Composition". Cite journal requires