1 See, for similar but more inclusive definitions, van der Burg, W., ‘The Slippery Slope Argument’, Ethics 102.1 (1991), pp. 42–65 (p. 42); Schauer, F., ‘Slippery Slopes’, Harvard Law Review 99.2 (1985), pp. 361–3 (pp. 364–5). For a similar but narrower definition, see La Follette, H., ‘Living on a Slippery Slope’, Journal of Ethics 9.3–4 (2005), pp. 475–99 (pp. 475–82).
2 Kamisar, Y., ‘Some Non-Religious Views against Proposed “Mercy Killing” Legislation’, Minnesota Law Review 42.6 (1958), pp. 969–1042 (pp. 975–7).
3 Bollinger, L. C., ‘The Skokie Legacy: Reflections on an “Easy Case” and Free Speech Theory’, Michigan Law Review 80.4 (1982), pp. 617–33; Neier, A., Defending My Enemy: American Nazis, the Skokie Case, and the Risks of Freedom (New York, 1979), esp. at. p. 124.
4 Olson, J. E. and Kopel, D. B., ‘All the Way down the Slippery Slope: Gun Prohibition in England and Some Lessons for Civil Liberties in America’, Hamline Law Review, 22.2 (1999), pp. 399–465.
5 van der Burg, ‘The Slippery Slope Argument’, p. 59.
6 Schubert, L., ‘Ethical Implications of Pharmacogenetics – Do Slippery Slope Arguments Matter?’, Bioethics 18.4 (2004), pp. 361–77 (pp. 368–9).
7 See, for example, Walton, D., Slippery Slope Arguments (Oxford, 1992), pp. 101–2; Häyry, H., ‘How to Assess the Consequences of Genetic Engineering’, Ethics and Biotechnology, ed. Harris, J. and Dyson, A. (London, 1994), pp. 144–56; Launis, V., ‘Human Gene Therapy and the Slippery Slope Argument’, Medicine, Health Care and Philosophy 5 (2002), pp. 169–79; La Follette, ‘Living on a Slippery Slope’.
8 See, for example, Keown, J., ‘Euthanasia in The Netherlands: Sliding down the Slippery Slope’, Notre Dame Journal of Law, Ethics and Public Policy 9 (1995), pp. 407–48; Jochemsen, H. and Keown, J., ‘Voluntary Euthanasia under Control? Further Empirical Evidence from The Netherlands’, Journal of Medical Ethics 25.1 (1999), pp. 16–21.
9 EP is stronger than the empirical claim sometimes made by empirical SSAs, which may be of the form ‘our descendants might do Extreme’ or ‘our descendants are likely to do Extreme’. However, since I will later assume that EP is true, I adopt the strongest version here in order to be as charitable as possible to the proponents of empirical SSAs.
10 For a related objection, see Rizzo, M. J. and Whitman, D. G., ‘The Camel's Nose Is in the Tent: Rules, Theories, and Slippery Slopes’, UCLA Law Review 51 (2003), pp. 539–92 (pp. 543, 572–3).
11 Rice, N. L., A Debate on Slavery (New York, 1846), p. 33.
12 See, for this argument, Rifkin, J., Algeny: A New Word – A New World (Harmondsworth, 1984), pp. 219–44, esp. pp. 231–3, 237, 244; Tännsjö, T., ‘Should We Change the Human Genome?’, Theoretical Medicine and Bioethics 14.3 (1993), pp. 231–47; G. J. Annas, ‘Genism, Racism, and the Prospect of Genetic Genocide’, paper presented at the World Conference against Racism, Racial Discrimination, Xenophobia and Related Intolerance, Durban (2001).
13 Elga, A., ‘Reflection and Disagreement’, Noûs 41.3 (2007), pp. 478–502 (p. 479).
14 We should perhaps extend this line of thinking to all possible people. See Kelly, T., ‘The Epistemic Significance of Disagreement’, Oxford Studies in Epistemology, vol. 1, ed. Gendler, T. Szabo and Hawthorne, J. (Oxford, 2005), pp. 167–96.
15 Whether we should take disagreement from an epistemic peer as evidence for the falsity of our beliefs has been a topic of much recent discussion. See, for example, Christensen, D., ‘Epistemology of Disagreement: The Good News’, Philosophical Review 116 (2004), pp. 187–217; Kelly, ‘The Epistemic Significance of Disagreement’; Elga, ‘Reflection and Disagreement’.
16 PA is a variant of what Derek Parfit calls the instrumental version of the Present Aim Theory. See Parfit, D., Reasons and Persons (Oxford, 1984), p. 117. Though Parfit does not defend this view, others have defended something close to it. See, for example, Williams, B., ‘Internal and External Reasons’, in his Moral Luck (Cambridge, 1981), pp. 101–13.
17 It will provide some evidence if there is evidence of either a negative or positive correlation between these contingent facts.
18 Volokh, E., ‘The Mechanisms of the Slippery Slope’, Harvard Law Review 116.4 (2003), pp. 1026–1137 (pp. 1056–8).
19 de Wert, G. and Mummery, C., ‘Human Embryonic Stem Cells: Research, Ethics and Policy’, Human Reproduction 18.4 (2003), pp. 672–82 (p. 675).
20 Volokh, ‘Mechanisms’, pp. 1041–3.
21 For examples of arguments where such a premise is made explicit, see Clark, M., ‘Euthanasia and the Slippery Slope’, Journal of Applied Philosophy 15.3 (1998), pp. 251–7; Enoch, D., ‘Once You Start Using Slippery Slope Arguments, You're on a Very Slippery Slope’, Oxford Journal of Legal Studies 21.4 (2001), pp. 629–47.
22 Though see, for doubts about the corruptingness of addiction, Becker, G. S. and Murphy, K. M., ‘A Theory of Rational Addiction’, Journal of Political Economy 96.4 (1988), pp. 675–700; Foddy, B. and Savulescu, J., ‘Addiction and Autonomy: Can Addicted People Consent to the Prescription of their Drug of Addiction?’, Bioethics 20.1 (2006), pp. 1–15.
23 Many thanks to Guy Kahane, Julian Savulescu, Andrew Reisner, Roger Crisp, Nick Bostrom, Rebecca Roache, Bill Child, Ingmar Persson, an audience at the University of Oxford, and two anonymous reviewers for their comments on drafts of this article. I thank the Wellcome Trust (grant number WT077879) and Christ Church for their funding.