In This Article Expand or collapse the "in this article" section Mereology

  • Introduction
  • General Overviews
  • Anthologies
  • Composition as Identity
  • Mereotopology

Philosophy Mereology
Paul R. Daniels
  • LAST REVIEWED: 22 November 2022
  • LAST MODIFIED: 27 July 2016
  • DOI: 10.1093/obo/9780195396577-0313


Mereology concerns part-whole relations, which is to say that mereological discussions focus on (1) the relation between the parts of a whole and the whole of which they’re a part, and (2) the relations between the parts within a whole. But mereological discussions extend beyond mere articulation of mereological axioms. Mereologies—or part-whole theories—play a central role in many aspects of metaphysics. While this has been the case since the time of the Stoics, there has recently been a noteworthy revival of interest in mereology. Some are interested in mereology out of a genuine interest in the field itself, whereas others turn to it to find a toolkit to help them tackle problems that arise in other discussions, as many problems, it turns out, feature a mereological component. Mereology has, for instance, played a key role in motivating a variety of views. Do, for instance, any two objects “mereologically fuse” to form a further object? Some cases seem clear, like the molecules in my body and me; other more gerrymandered cases, like your nose and the Eiffel Tower, seem less clear. Our mereological views here—whether we want to be mereological nihilists, universalists, or restricted composition theorists—will, at a minimum, play a crucial role in forming our ontological commitments. Also notice that while mereological discussion typically focuses on material entities, sometimes our interests gravitate toward the mereological structure of space-time regions, or to the relations that hold between regions and the objects that occupy them, or to the mereology of such entities as events. Mereology has its fingers in many pies. But no matter how we might want to answer mereological concerns, we might further wonder if this is putting the cart before the horse. That is, should mereology take priority? Or should we work out which metaphysical theses we want to defend, and then determine which mereological principles best serve our ends? Different authors take different position here. This article highlights many of the key mereological concepts and principles, but it also outlines some of the fundamental problems that confront philosophers who think about mereology. The article also focuses on philosophical issues, rather than formal ones. For the sake of accessibility, this article avoids technical presentations of, for instance, mereological axioms. It’s also noteworthy that there is a nontrivial contribution to mereology from non-English writers, especially from Eastern Europe.

General Overviews

While there are no introductory textbooks on mereology, there are a number of good introductions, surveys, and general overviews of the field. Varzi 2016 stands out in this regard, as it is detailed, up-to-date, extensive, and clearly written. Simons 1987 assumes little on the part of the reader, and is worth reading in its entirety given the central place it holds in contemporary discussions of mereology. In addition, the introductory chapters of the anthologies on mereology can play the right role for readers interested in particular topics; for example, those unfamiliar with mereology who have a particular interest in locative relations would find the introduction to Kleinschmidt 2014 (cited under Anthologies) a good place to start.

  • Simons, Peter. Parts: A Study in Ontology. Oxford: Oxford University Press, 1987.

    The first three chapters of this contemporary locus classicus on parthood act as an excellent introduction to mereology.

  • Varzi, Achille. “Appendix: Formal Theories of Parthood.” In Mereology and the Sciences. Edited by Claudio Calosi and Pierluigi Graziani, 259–370. Berlin: Springer, 2014.

    This is a succinct technical overview of many mereological principles and the ways in which they’re connected. A valuable reference to have on hand.

  • Varzi, Achille. “Mereology.” In The Stanford Encyclopedia of Philosophy. Edited by Edward Zalta. Stanford, CA: Stanford University, 2016.

    Surveys the range of standard mereological principles, with an emphasis on the contemporary, and gradually introduces formal presentations. Varzi also highlights the controversies and problems in the process. A comprehensive introduction, with an extensive bibliography.

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