Skip to main content

Intertemporal Disagreement and Empirical Slippery Slope Arguments


One prevalent type of slippery slope argument has the following form: (1) by doing some initial act now, we will bring it about that we subsequently do some more extreme version of this act, and (2) we should not bring it about that we do this further act, therefore (3) we should not do the initial act. Such arguments are frequently regarded as mistaken, often on the grounds that they rely on speculative or insufficiently strong empirical premises. In this article I point out another location at which these arguments may go wrong: I argue that, in their standard form, the truth of their empirical premises constitutes evidence for the falsity of their normative premises. If we will, as predicted, do the further act in the future, this gives us at least a prima facie reason to believe that the performance of this further act would be good, and thus something we should try to bring about. I end by briefly assessing the dialectic implications of my argument. I delineate a subset of slippery slope arguments against which my objection may be decisive, consider how the proponents of such arguments may evade my objection by adding further premises, and examine the likely plausibility of these additional premises.

    • Send article to Kindle

      To send this article to your Kindle, first ensure is added to your Approved Personal Document E-mail List under your Personal Document Settings on the Manage Your Content and Devices page of your Amazon account. Then enter the ‘name’ part of your Kindle email address below. Find out more about sending to your Kindle. Find out more about sending to your Kindle.

      Note you can select to send to either the or variations. ‘’ emails are free but can only be sent to your device when it is connected to wi-fi. ‘’ emails can be delivered even when you are not connected to wi-fi, but note that service fees apply.

      Find out more about the Kindle Personal Document Service.

      Intertemporal Disagreement and Empirical Slippery Slope Arguments
      Available formats
      Send article to Dropbox

      To send this article to your Dropbox account, please select one or more formats and confirm that you agree to abide by our usage policies. If this is the first time you use this feature, you will be asked to authorise Cambridge Core to connect with your <service> account. Find out more about sending content to Dropbox.

      Intertemporal Disagreement and Empirical Slippery Slope Arguments
      Available formats
      Send article to Google Drive

      To send this article to your Google Drive account, please select one or more formats and confirm that you agree to abide by our usage policies. If this is the first time you use this feature, you will be asked to authorise Cambridge Core to connect with your <service> account. Find out more about sending content to Google Drive.

      Intertemporal Disagreement and Empirical Slippery Slope Arguments
      Available formats
Hide All

1 See, for similar but more inclusive definitions, van der Burg, W., ‘The Slippery Slope Argument’, Ethics 102.1 (1991), pp. 4265 (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. 9691042 (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. 399465.

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. 1621.

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. 478502 (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. 187217; 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. 10261137 (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. 675700; 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. 115.

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.

Recommend this journal

Email your librarian or administrator to recommend adding this journal to your organisation's collection.

  • ISSN: 0953-8208
  • EISSN: 1741-6183
  • URL: /core/journals/utilitas
Please enter your name
Please enter a valid email address
Who would you like to send this to? *


Full text views

Total number of HTML views: 6
Total number of PDF views: 97 *
Loading metrics...

Abstract views

Total abstract views: 331 *
Loading metrics...

* Views captured on Cambridge Core between September 2016 - 25th March 2018. This data will be updated every 24 hours.