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Almost Identical, Almost Innocent
Published online by Cambridge University Press: 03 July 2018
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.
- Copyright © The Royal Institute of Philosophy and the contributors 2018
1 Lewis, David, Parts of Classes (Oxford, and Cambridge MA: Basil Blackwell Ltd., 1991), viiGoogle Scholar.
2 Lewis, David, ‘Mathematics is Megethology’, Philosophia Mathematica 1 (1993), 3–23CrossRefGoogle Scholar, 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)Google Scholar, 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.
6 Katherine Hawley, ‘Ontological Innocence’, in Composition as Identity, 70–89.
7 Lewis, Parts of Classes, 82.
9 Lewis, Parts of Classes, 82,
10 Armstrong, D.M., Universals and Scientific Realism II (Cambridge: Cambridge University Press, 1980), 37–38Google Scholar.
11 Lewis, Parts of Classes, 73.
13 Van Inwagen, ‘Composition as Identity’, 214–5.
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): 38–42Google Scholar. Bradley, F.H., ‘On Professor James' Doctrine of Simple Resemblance’, Mind 2 (1893), 83–88CrossRefGoogle Scholar.
19 For examples, see Denkel, Arda, ‘Resemblance Cannot Be Partial Identity’, Philosophical Quarterly 48 (1998): 200–204CrossRefGoogle Scholar, Baxter, D.L.M., ‘Instantiation as Partial Identity’, Australasian Journal of Philosophy 79/4 (2001): 449–64Google Scholar, and Mantegani, Nicholas, ‘Instantiation is Not Partial Identity’, Philosophical Studies 163/3 (2013), 697–715CrossRefGoogle Scholar.
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)Google Scholar 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)Google Scholar https://plato.stanford.edu/archives/fall2017/entries/location-mereology/ and Kleinschmidt, Shieva ‘Introduction’ to Mereology and Location (ed.) Kleinschmidt, (Oxford University Press, 2014)CrossRefGoogle Scholar.
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.
32 Hawley, Katherine, ‘David Lewis on Persistence’, in Loewer, B. and Schaffer, J. (eds), A Companion to David Lewis (2015)Google Scholar.
34 I am grateful to Aaron Cotnoir for his helpful advice.