Defeaters and practical knowledge


This paper situates the problem of defeaters in a larger debate about the source of normative authority. It argues in favour of a constructivist account of defeasibility, which appeals to the justificatory role of normative principles. The argument builds upon the critique of two recent attempts to deal with defeasibility: first, a particularist account, which disposes of moral principles on the ground that reasons are holistic; and second, a proceduralist view, which addresses the problem of defeaters by distinguishing between provisional and strictly universal principles. The particularist view fails to establish that moral principles have no epistemological import, but it raises important questions about their role in practical reasoning. The proceduralist view fails to distinguish between reasoning by default and reasoning by principles, but it shows that normative principles have a structural justificatory role. The constructivist view recognizes that the moral valence of normative claims vary across contexts, but denies that this is because of holism about reasons. Rather, it defends defeasibility within a constructivist account of reasoning where universality serves as the matrix of judgment. The constructivist view vindicates the justificatory role of universal normative principles, and makes room for some ordinary sources of defeasibility, which are left unaccounted by competing views, and which depend on the agent’s own progress.

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  1. 1.

    This is an adaptation of the famous example about borrowed arms in Plato’s Republic.

  2. 2.

    In some cases, the lack of normative determinacy is better understood as a failure of normative determinacy. In either case, the definition I offer is opposed to defeasibility as a failure of representation, see Redondo (2012). Redondo holds that moral realism, which considers moral reasons as facts, does not admit of defeaters: Either a consideration is a reason for something, or it is not. Redondo’s characterization has the unfortunate consequence of ruling out moral realists who are in favor of particularism.

  3. 3.

    I name only a few forms of normative failure, but the list is not meant to be exhaustive, see the pioneering work on the subject in Nozick (1968).

  4. 4.

    For an informal definition of rebutting and undercutting defeaters, see Horty ; Horty (2007; 2014, pp. 50–51). cf. Pollock (1986, 1987). Horty distinguishes three accounts of reasoning by default rules. In the fixed priority theory, priority relations are fixed in advance, and all the defaults are universally applicable; in the variable priority default logic, the priority ordering is also defeasible; in the exclusionary default logic, default logic is used to determine whether certain default rules are to be excluded from consideration entirely. This latter case deploys a different sense of defeasibility, but I do not think the difference is as fundamental as suggested in Redondo (2012, p. 320). In any case, this difference does not affect my argument. A concern that I have about Horty’s proposal is whether defeasibility may be preserved in a non-monotonic reasoning if the normative relations among reasons and defeaters are governed by fixed priority rules. I will consider the implications of admitting moral defeaters for moral authority, without entering the normative debate about which kinds of defeaters, and how they are logically organized. These issues pertain to a formal account of the normative theory of reasons, which is beyond the scope of this essay.

  5. 5.

    Among undercutting defeaters there are defeaters that show how some kinds of reasons do not apply in some contexts, because they are the wrong kind of reason.

  6. 6.

    This is Dancy’s position: “It is not as if it is some reason for me to believe that there is something red before me, though that reason is overwhelmed by contrary reasons. It is no longer any reason at all to believe that there is something red before me; indeed it is a reason for believing the opposite” (Dancy 2004, p. 74). See also Dancy (1993, pp. 84–86), Wiggins (1993), Horty (2014, p. 152). Particularists often recognize that broad generalities are relevant e.g. in moral education and conversation, see e.g. Little (2000).

  7. 7.

    For an argument that justifies moral particularism on the basis of holism about general reasons (Dancy 1993, pp. 84–86; 2006, p. 7; Wiggins 1993; Lance and Little 2008). For Recent arguments that dispute the relation between holism and particularism see Millgram (2005), Väyrynen (2006, 2009), McKeever and Ridge (2005, 2006), Schroeder (2011), Darwall (2013).

  8. 8.

    I share Dancy’s view that moral reasons have the same status as other normative reasons, see Dancy (2006, p. 132). I do not argue that moral obligations differ from other sorts of obligations because of their special content or status.

  9. 9.

    This expression is Scanlon (1998, p. 17). But it has become current in debates about reasons, and routinely deployed as a primitive (that is, not further analyzable) term in practical reasoning.

  10. 10.

    I take “relevant agents” here to mean agents that are capable of understanding what moral obligations operate and how they applied to them. In short, this means agents capable of responsibility. For the purpose of this argument, further qualifications are not necessary.

  11. 11.

    On the force of this argumentative move, see also Holton (2002) and Millgram (2005).

  12. 12.

    For instance, McKeever and Ridge (2005, 2006) argue that holism presupposes generalism. On the claim that reason holism is compatible with generalism, see also Cullity and Holton (2002), Holton (2002), Schroeder (2011), Horty (2014, p. 153).

  13. 13.

    I suppose this is what Millgram calls “the defusing move,” not quite an argument (Millgram 2005).

  14. 14.

    See Helm (1968). To some extent, the claim is analogous to the claim about the shapelessness of the moral in respect to the natural. The “shape” of a concept refers to the real similarity between all, and only the things that fall under it. The claim admits to different formulations, but it is generally invoked to explain the phenomenon that the extensions of evaluative terms and concepts seem to outrun non-evaluative classifications, see Kirchin (2010). For instance, McDowell holds that there is no guarantee that the extensions of evaluative terms or concepts are “shapely” in the sense that they correspond to kinds into which things can in principle be seen to fall independently of an evaluative outlook” (McDowell 1981, p. 216; Dancy 1993, pp. 84–86; Wiggins 1993; Little 2000; Kirchin 2010).

  15. 15.

    For instance, Stephen Darwall regards this analogy as limited to the concept of moral obligation, but recognizes an asymmetry between legal and moral contexts, see Darwall (2013, pp. 172–173).

  16. 16.

    I leave aside the complexity of the legal case. There is a disagreement about the source of legal authority. In contrast to legal positivism, some argue that the legitimacy of law must refer to moral principles. Furthermore, in legal contexts there is a further distinction to draw between principles and rules, see Redondo (2005).

  17. 17.

    It is undeniable that there are institutional and conventional aspects of morality; the issue is whether moral obligations rest solely on convention. See e.g. Williams (1985).

  18. 18.

    Ross (1930, p. 20). I believe that it is a mistake to conflate the nature and normative status of the all-things-considered judgment and the normative status of prima facie duties that are thereby defeated, see Bagnoli (2007); see also Williams (1963, pp. 184–185).

  19. 19.

    Williams criticizes ethical theories for failing to account for regret, “basically because they eliminate from the scene the ‘ought not acted upon’,” (Williams 1963, p. 175). The thought is pursued in Dancy (1993, Chap. 7). By contrast, for Hare prima facie duties are defeasible rules, which can be overridden in deliberation, without leaving a moral remainder. Since such rules are associated to deontic emotions (e.g. guilt and regret), this explains why such emotions are present even after the moral conflict is resolved (Hare 1981, p. 39). For an account of moral residue in a balancing structure, see Nozick (1981, p. 489). I consider this debate in some detail in Bagnoli (2007).

  20. 20.

    I consider a very simple example of balancing structure, but things get complicated very soon: See Nozick (1968; 1981, pp. 479–494). Despite the elegance and depth of Nozick’s account, I think that my objection applies, which is that moral obligation resists this treatment.

  21. 21.

    Broome’s balancing structure does not use numbers, and thus it is not additive. However, it is not clear to me by what more “sophisticated function” it generates aggregates. I suspect that there is no answer to this question, but reservations concern the overall project, which aims to determine action by producing aggregates of reasons. I believe it is misguided. On measurement of moral weight, see Nozick (1981, pp. 490–492).

  22. 22.

    This view is defended in Darwall (2013). In Sect. 10, I will briefly comment on this strategy, and explain why the constructivist account I propose is preferable.

  23. 23.

    Kantian constructivism names a rather diversified cluster of theories, which differ as to the scope and aims of construction. For an overview of the varieties of Kantian constructivism, see Bagnoli (2011, §1–2).

  24. 24.

    See O’Neill (1996, p. 85). This claim has been often defended in proceduralist terms, see e.g. “The procedural moral realist thinks that there are answers to moral questions because there are correct procedures for arriving at them. But the substantive moral realist thinks that there are correct procedures for answering moral questions because there are moral truths or facts” (Korsgaard 1996, pp. 36–37).

  25. 25.

    Korsgaard’s argument against the application model builds upon two distinct claims. First, the claim that cognitions of a piece of reality cannot be “compelling:” “For think how that account would have to work. The agent would have to recognize it, as some sort of eternal normative verity, that it is good to take the means to his ends. How is this verity supposed to motivate him?” (Korsgaard 2003, p. 110; 1996, pp. 16, 38–40). Second, the claim that for whatever moral principle stating what to do, the question arises whether and how it applies. “If it is just a fact that a certain action would be good, a fact that you might or might not apply in deliberation, then it seems to be an open question whether you should apply it” (Korsgaard 2003, p. 112; 1996, pp. 44–47). I criticise Korsgaard’s argument in Bagnoli (2013). For present purposes, only the second claim is relevant.

  26. 26.

    Korsgaard’s argument draws on an analogy with maps: “If to have knowledge is to have a map of the world, then to be able to act well is to be able to decide where to go and to follow the map in going there. The ability to act is something like the ability to use the map, and that ability cannot be given by another map. [...] goodness in action cannot just be a matter of applying our knowledge of the good—not even a matter of applying our knowledge of what makes action itself good. This is because the ability to apply knowledge presupposes the ability to act” (Korsgaard 2003, p. 110). The analogy is problematic on its own, but this is a side issue here.

  27. 27.

    On a more robust conception of construction, constructivism qualifies as a distinct form of rational justification, which is alternative to practical inference.

  28. 28.

    “Deciding which cases are which is, of course, a deliberative problem and that is an issue on which principles give no guidance at all. Principles tell us nothing about where or when they are to be applied” (Lebar 2013, p. 192).

  29. 29.

    This is Richard Hare’s argument in support of prima facie duties at the ordinary level of moral thinking, see Hare (1981, Chap. 1). The term “summary rules” is introduced by John Rawls in contrast to the “practice” conception of principles, see Rawls (1955).

  30. 30.

    Millgram also argues that the strategy of institutionalizing exceptions produces perverse results, insofar as it raises the complexity of the principles of action. As already noted by Hare and Nozick, complex principles are not only hard to formulate, but also difficult to learn. Their efficacy is doubtful.

  31. 31.

    This is one of Dancy’s objections against reasoning by principles, see Dancy (2004, p. 64). I consider Dancy’s objection in the context of the dispute about moral perception, see Bagnoli (2011b, especially p. 96).

  32. 32.

    I take much for granted here. For a thorough discussion of universality as the criterion of rational knowledge and action, see Engstrom (2009). I agree with much of the argument that Engstrom offers in support of situating Kant’s appeal to the universal law in the tradition of practical cognitivism. I also share Engstrom’s view that a constructivist account of practical reason serves the purpose of vindicating the objectivity of practical knowledge, see Engstrom (2013).

  33. 33.

    On the Kantian view of reason as the source of authority of moral principles, see Bagnoli (2013), O’Neill (2015).

  34. 34.

    Elijah Millgram forcefully makes the point: “Making an exception and building an exception-shaped twiddle into a rule work differently in a social world” (Millgram 2005, p. 103).

  35. 35.

    One may object that there are established practices of “institutionalizing exceptions,” e.g. “Theatre tickets are $5, except for senior citizens.” However, in this case, it is preferable to say that for the category citizen the rule does not range over the class of seniors citizens. The scope of application of principles may be broad or narrow (including large numbers of individuals or a singleton), but this is a different matter than the relation that principles bear to their exceptions.

  36. 36.

    Millgram considers a fundamental flaw of Kantian theory that it cannot accommodate the need for exceptions (Millgram 2005, p. 108). He regards exceptions as “necessary preconditions for successful agency” (Millgram 2005, Chap. 5 §4.5). This is where Millgram and I part ways. He offers a theory of practical reasoning that is a viable alternative to Kantian constructivism, but I cannot take it into account here.

  37. 37.

    On the distinction between being “obligated,” and being “obliged,” see Hart (1961, pp. 6–8).

  38. 38.

    Obstruction may depend on the interference of others. This is a complex case, which would require special consideration, but I have to set it aside.

  39. 39.

    The issue is “the amount of detail about the agents’ circumstances and his proposed action which can be included in the maxim” (O’Neill 1975, p. 37). A maxim is a practical principle underlying action in contrast to aspects of the action that are below the level of intention (sub-personal processes), and also in contrast to more specific intentions, see O’Neill (1989, pp. 129, 151–152, 158).

  40. 40.

    To address the problem of the relevant descriptions, Barbara Herman argues that the CI-procedure applies psychologically to actual intention underlying the action, and produces a recognizable pattern of moral actions only insofar as the agents’ psychology is relevantly similar. She stresses the psychological underpinning of the theory by introducing criteria of moral salience that help moral reasoning to be effective, see Herman (1993, Chap. 4, Chap. 3 §3, and Chap. 7 §4). There are two serious problems with Herman’s proposal. First, on her account, the categorical imperative procedures constrain only agents who are already endowed with a moral sensibility and leaves the non-moral ones unconstrained. Second, as Millgram puts it, the “necessary but totally unaccounted for regimentation of agents’ motivational structure has become the engine of the theory” (Millgram 2005, p. 128 n. 39). For these reasons, Herman’s solution to the problem does not seem to be congruent with the Kantian theory of practical reasoning, insofar as it is grounded in empirical psychology. The criteria of salience are a dubious basis for moral consensus and may undermine the autonomy of reason. For this very reason, Herman’s account of practical reasoning does not qualify as constructivist, see Herman (1993, pp. 152–153). There is something to be said about the role of moral sensibility in practical reasoning, but it cannot be put in terms of criteria of moral salience.

  41. 41.

    Ross (1939, pp. 168–171). On this point, see Dancy (1993, p. 95). Lebar (2013) pursues this line, refreshing the often forgotten connection between Ross’ intuitionism and Aristotelian ethics.

  42. 42.

    See Kant’s argument for the categorical imperative, Kant Ak 5.19–30. Cf. Rawls (1980), Engstrom (2009, 2013).

  43. 43.

    The requirement of autonomy excludes all thinking and acting that depend on “the contingent, subjective conditions that distinguish one rational being from another” (Kant Ak 5.21).

  44. 44.

    The qualification “moral” in these cases does not add anything that helps elucidate the authority of such reasons. The authority of moral reasons is the very same authority as the authority of reasons. There is no explicative role to play for “morality” understood as an eminent domain of special objects.

  45. 45.

    “Reason grants respect only to that which has been able to withstand its free and public examination” (Kant Axi, see also A738/B766). See O’Neill (1989, 2015). To avoid some possible confusion, I do not take this conclusion to count against Scanlon’s view of what it takes to be realistic about reasons.


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I would like to thank Robert Audi, Giovanna Corsi, Maria Luisa Dalla Chiara, Roberto Giuntini, Elijah Millgram, Nino Rotolo, the referees and the editors of this volume. Work on this paper has been possible thanks to the support of the Department of Philosophy, Classics, History of Art and Ideas at the University of Oslo.

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Bagnoli, C. Defeaters and practical knowledge. Synthese 195, 2855–2875 (2018).

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  • Defeater
  • Kantian constructivism
  • Moral particularism
  • Reason holism
  • Obligation
  • Universality