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Published online by Cambridge University Press:  12 February 2014

Justin Weinberg*
Philosophy, University of South Carolina


Must principles of justice be practical? Some political philosophers, the “implementers,” say yes. Others, the “idealists,” say no. Despite this disagreement, the implementers and idealists agree on what “practical” means, subscribing to the “implementation-prediction” (IP) conception of practicality. They also seem to agree that principles of so-called “ideal theory” need not be (and often are not) IP-practical. The implementers take this as a reason to reject ideal theory as an approach to principles of justice, while the idealists do not. In this paper, I argue that we should reject the IP conception of practicality. The implementers make a mistake, then, by requiring principles of justice to be IP-practical. But the idealists make a mistake, too, by rejecting in general the requirement that principles of justice be practical. For there is a plausible alternative conception of practicality that political philosophers should accept: the “experimentation-learning” (EL) conception. EL-practicality makes for a more realistic and epistemically accessible standard of practicality, and thus should be welcomed by the realistically-inclined implementers. It also preserves a crucial role for ideal theory, so should be welcomed by the idealists, too.

Research Article
Copyright © Social Philosophy and Policy Foundation 2013 

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I would like to thank David Schmidtz, Carmen Pavel, Rosie Johnson, and several anonymous referees for helpful written comments on an earlier draft of this essay. I am also grateful to the other contributors to this volume for their critical comments and discussion of these ideas. A version of the essay was delivered at the Midsouth Philosophy Conference in Memphis, Tennessee in February of 2013, and I would like to thank my audience there and my commentator, Ashley Acosta-Fox, for their questions and comments.


1 Rawls, John, The Law of Peoples (Cambridge, MA: Harvard University Press, 2001), 7Google Scholar. Also see the discussion of “optimization” as the “confrontation of desirability with feasibility considerations” in Brennan, Geoffrey, “Feasibility in Optimizing Ethics,” Social Philosophy and Policy 30, nos. 1-2 (2013): 314CrossRefGoogle Scholar.

2 In Section III, I explain how G. A. Cohen and David Estlund are idealists in this sense.

3 The views of specific implementers are described in Section II.

4 For a similar spectrum, see Farrelly, Colin, “Justice in Ideal Theory: A Refutation,” Political Theory 55, no. 4 (2007): 844–64Google Scholar.

5 The reader should assume that subsequent references to practicality are to substantive practicality, unless otherwise noted.

6 The distinction between formal and substantive practicality is important because it clears up a vagueness that can be confusing. See, for example, the discussion in Section III.

7 For some general discussions of the distinction, see Valentini, Laura, “Ideal vs. Non-Ideal Theory: A Conceptual Map,” Philosophy Compass 7, no. 9 (2012): 654–64CrossRefGoogle Scholar; Simmons, A. John., “Ideal and Nonideal Theory,” Philosophy and Public Affairs 38, no. 1 (2010): 536CrossRefGoogle Scholar; Schmidtz, David, “Nonideal Theory: What It Is and What It Needs To Be,” Ethics 121, no. 4 (2011): 772–96CrossRefGoogle Scholar.

8 My conception of ideal theory is based largely on what I take to be Rawls's view. See Rawls, John, A Theory of Justice, rev. ed. (Cambridge, MA: Harvard University Press, 1999), 78Google Scholar. See also p. 4 on well-ordered society; p. 125, on strict compliance; and pp. 215ff on nonideal theory.

9 Justin Weinberg, “A Little Reality is a Dangerous Thing” (unpublished manuscript).

10 See Farrelly, “Justice in Ideal Theory: A Refutation.”

11 Mills, Charles W., “Rawls on Race/Race in Rawls,” Southern Journal of Philosophy 47, no. 1 (2009): 161–84CrossRefGoogle Scholar. Also see Mills, , “‘Ideal Theory’ as Ideology,” Hypatia 20 (2005): 165–84Google Scholar.

12 Murphy, Liam, “Institutions and the Demands of Justice,” Philosophy and Public Affairs 27, no. 4 (1998): 251–91CrossRefGoogle Scholar.

13 Sandel, Michael, Liberalism and the Limits of Justice (Cambridge: Cambridge University Press, 1982)Google Scholar.

14 Robeyns, Ingrid, “Ideal Theory in Theory and Practice,” Social Theory and Practice 34 no. 3 (2008): 341–62, at 361CrossRefGoogle Scholar.

15 Sen, Amartya, The Idea of Justice (Cambridge, MA: Harvard University Press, 2009)Google Scholar.

16 Wiens, David, “Prescribing Institutions without Ideal Theory,” Journal of Political Philosophy 20, no. 1 (2012): 4570, at 67CrossRefGoogle Scholar.

17 Cohen, G. A., Rescuing Justice and Equality (Cambridge, MA: Harvard University Press, 2008), 84CrossRefGoogle Scholar.

18 Ibid., 86.

19 Estlund, David, “Human Nature and the Limits (if any) of Political Philosophy,” Philosophy and Public Affairs 39, no. 3 (2011): 207–37, at 226CrossRefGoogle Scholar.

20 “The content of justice … might … precede any facts about what humans or any beings happen to be like” (Estlund, “Human Nature,” 229), including facts about their altruistic tendencies or abilities to comply with particular laws or support particular institutions.

21 Estlund, David, Democratic Authority (Princeton, NJ: Princeton University Press, 2008), 264–67Google Scholar.

22 Cohen, Rescuing Justice, 271.

23 Ibid., 301.

24 Fundamental principles of justice, according to Cohen, are “in no way dependent on the character of any facts.” Ibid., 281.

25 Ibid., 272.

26 Estlund, Democratic Authority, 268.

28 Ibid., 266.

31 Cohen, Rescuing Justice, 268.

32 As a reminder, unless otherwise noted, “practical” refers to “substantively practical.”

33 If you object to using the term “correct” to describe principles of justice, substitute “most acceptable” for it.

34 Again, this point is neutral between realist and constructivist accounts of evaluative standards. We could be revising our standards in an attempt to achieve mere reflective equilibrium, or we could think that it is only through investigation that we have a chance of properly identifying the mind-independently true evaluative standards. If we are constructivists of some sort, then of course we would need to try them out to agree on them in any informed way. But if we are realists, that the principles seemed right to us when we tried them would merely be good evidence that we have discovered the right principles. Given that we are often wrong in our predictions about what works, we should not trust our armchair judgments.

35 Sen, Amartya, Inequality Reexamined (Cambridge, MA: Harvard University Press 1992) chap. 1Google Scholar.

36 My view on these matters is influenced by Millgram, Elijah, Practical Induction (Cambridge, MA: Harvard University Press, 1997)Google Scholar and Richardson, Henry, Practical Reasoning about Final Ends (Cambridge: Cambridge University Press, 1994)CrossRefGoogle Scholar.

37 Discussed in Weinberg, “A Little Reality is a Dangerous Thing.”

38 Note that changing the language from “impossible” to “unlikely” does not help the implementers, as likelihood is going to be prospectively judged, based on an interpretation of the facts—an interpretation we have reason to distrust.

39 Derek Parfit famously says of nonreligious ethics, that, because it is so young a science, “it is not irrational to have high hopes” for its success. Parfit, , Reasons and Persons (New York: Oxford University Press, 1984), 453–54Google Scholar. I add here that because it is so young, it might be unreasonable to think that it has already succeeded.

40 Brandeis, Louis J.. New State Ice Co. v. Liebmann (dissenting), 285 U.S. 311 (1932)Google Scholar.

41 This version of the objection was put to me by Chris Bertram.