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Almost Identical, Almost Innocent

  • Katherine Hawley (a1)

In his 1991 book, Parts of Classes, David Lewis discusses the idea that composition is identity, alongside the idea that mereological overlap is a form of partial identity. But this notion of partial identity does nothing to help Lewis achieve his goals in that book. So why does he mention it? I explore and resolve this puzzle, by comparing Parts of Classes with Lewis's invocation of partial identity in his 1993 paper ‘Many But Almost One’, where he uses it to address Unger's problem of the many. I raise some concerns about this way of thinking of partial identity, but conclude that, for Lewis, it is an important defence against accusations of ontological profligacy.

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1 Lewis, David, Parts of Classes (Oxford, and Cambridge MA: Basil Blackwell Ltd., 1991), vii.

2 Lewis, David, ‘Mathematics is Megethology’, Philosophia Mathematica 1 (1993), 323, at 3. Burgess, John P., ‘Lewis on Mereology and Set Theory’, in A Companion to David Lewis, (ed.) Loewer, Barry and Schaffer, Jonathan (Malden MA: Wiley-Blackwell, 2015), is a user-friendly guide to Lewis's writing on these topics, and includes a fetching attempt to make ‘mereoplethynticology’ happen. Karen Bennett, ‘“Perfectly Understood, Unproblematic, and Certain” Lewis on Mereology’, in the same volume, explores many of the themes I touch on in the present article.

3 Lewis, Parts of Classes, 73–74.

4 Ibid., 81.

5 Cotnoir, A.J. and Baxter, D.L.M. (eds), Composition as Identity (Oxford: Oxford University Press 2014).

6 Katherine Hawley, ‘Ontological Innocence’, in Composition as Identity, 70–89.

7 Lewis, Parts of Classes, 82.

8 Baxter, Donald L.M., ‘Identity in the Loose and Popular Sense’, Mind 97 (1988), 375–82, and Baxter, Donald L.M., ‘Many-One Identity’, Philosophical Papers 17 (1988), 193216.

9 Lewis, Parts of Classes, 82,

10 Armstrong, D.M., Universals and Scientific Realism II (Cambridge: Cambridge University Press, 1980), 3738.

11 Lewis, Parts of Classes, 73.

12 van Inwagen, Peter, ‘Composition as Identity’, Philosophical Perspectives 8 (1994), 207220 has illuminating remarks about Lewis's terminology here, in his footnote 2.

13 Van Inwagen, ‘Composition as Identity’, 214–5.

14 Ibid., 216.

15 Lewis, David, ‘Many, But Almost One’, pages references as republished in his Papers on Metaphysics and Epistemology (Cambridge: Cambridge University Press 1999).

16 Unger, Peter, ‘The Problem of the Many’, Midwest Studies in Philosophy 5 (1980), 411–67.

17 Lewis, ‘Many But Almost One’, 176.

18 Armstrong, D.M., ‘Reply to Lewis’, in Ontology, Causality and Mind: Essays in Honour of D.M. Armstrong, edited by Bacon, John, Campbell, Keith and Reinhardt, Lloyd (Cambridge University Press, 1993): 3842. Bradley, F.H., ‘On Professor James' Doctrine of Simple Resemblance’, Mind 2 (1893), 8388.

19 For examples, see Denkel, Arda, ‘Resemblance Cannot Be Partial Identity’, Philosophical Quarterly 48 (1998): 200204, Baxter, D.L.M., ‘Instantiation as Partial Identity’, Australasian Journal of Philosophy 79/4 (2001): 449–64, and Mantegani, Nicholas, ‘Instantiation is Not Partial Identity’, Philosophical Studies 163/3 (2013), 697715.

20 Lewis, ‘Many But Almost One’, 178.

21 Lewis, ‘Many But Almost One’, 178.

22 Lewis, ‘Elusive Knowledge’, Australasian Journal of Philosophy, 74, 549–67.

23 Schaffer, Jonathan, ‘Lewis on Knowledge Ascriptions’, in Loewer, and Schaffer, (eds), A Companion to David Lewis (Wiley-Blackwell 2015) is a helpful guide.

24 Lewis, ‘Many But Almost One’, 178.

25 Useful surveys of this material include Gilmore, Cody, ‘Location and Mereology’, Stanford Encylopedia of Philosophy (ed.) Zalta, E. (Fall 2017) and Kleinschmidt, ShievaIntroduction’ to Mereology and Location (ed.) Kleinschmidt, (Oxford University Press, 2014).

26 There may also be more complicated reasons to question the possibility of ordering by degree of mereological overlap, if gunk is actual; see Hudson, Hud, ‘Simples and Gunk’, Philosophy Compass 2.2 (2007) 291302.

27 Lewis, ‘Many But Almost One’, 178–9.

28 This type of ontic indeterminacy does not lead inevitably to ontic indeterminacy in existence, as I discuss in ‘Vague Existence’, Proceedings of the Aristotelian Society CII (2001–2), 125–40.

29 Lewis, David, On the Plurality of Worlds (Basil Blackwell, 1986), 212–13.

30 Markosian, Ned, ‘Brutal Composition’, Philosophical Studies 92/3 (1998), 211249.

31 Williamson, Timothy, Vagueness, (London: Routledge, 1994).

32 Hawley, Katherine, ‘David Lewis on Persistence’, in Loewer, B. and Schaffer, J. (eds), A Companion to David Lewis (2015).

33 As explored by e.g. Hawthorne, John, Metaphysical Essays (Oxford: Oxford University Press 2006), and Inman, Ross, ‘Neo-Aristotelian Plenitude’, Philosophical Studies 168/3 (2014), 583–97.

34 I am grateful to Aaron Cotnoir for his helpful advice.

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Royal Institute of Philosophy Supplements
  • ISSN: 1358-2461
  • EISSN: 1755-3555
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