Ethical theories may be said to be "Kantian" if they take their inspiration or focus from themes in the ethical theory of Immanuel Kant, while attempting something other than interpretation, development, or defense of Kant's own ethical theory. This is not a hard and fast distinction: What appears the right way to defend some thesis of Kant's to one may appear to another to be a complete departure from the crucial components of Kant's critical ethics. Moreover, some, like scholars Onora O'Neill (1975), Marcia Baron (1996), and Barbara Herman (1993), may see their work as exploring and defending the essential elements of Kant's moral theory, rather than developing an alternative theory inspired by him, even though they do not accept the metaphysical picture Kant thought crucial to his account. Many defenders of Kant's own account see the austere picture sometimes drawn of his ethics—as based on a rigoristic and formalistic obligation to duty —as mistaken, and argue that Kant's conception of what people are like as moral agents, and of what morality requires of people, is far richer and more satisfying than is often supposed. Still, it is useful to see Kantian theorists as holding that Kant had some crucial or seminal ethical matters right, while at the same time committing himself to claims or views that are from their perspective unacceptable. Thus, Kantian ethicists may be understood as attempting to rework cherished Kantian insights within the bounds of an overall more acceptable framework.
For many Kantian theorists, the point of departure from Kant is Kant's metaphysics and the role his metaphysical commitments play in his ethical theory. Kant struggled for a solution to the problem of how moral agents could be held responsible for their actions in a world governed by natural laws of cause and effect. If every event has a cause, which is itself caused, how could one see human action as anything but determined by the causes antecedent to it? And if human action is caused by natural law, in what sense can individuals see themselves as morally responsible?
Kant's solution to the problem drew on the metaphysical view developed in his Critique of Pure Reason, where he distinguished two worlds, one the world of sense—natural, physical, and empirical—and the other rational or "intelligible." The empirical world is governed by natural law, and effects do follow causes in ways determined by natural law. However, human beings are not merely natural but rational, and as members of the rational order are capable of "spontaneity": of producing effects based on determinations of reason, not causes. Because we have these two-fold natures, people occupy both worlds at once, and their actions are simultaneously subject to natural law and (as rational agents) to moral law.
Many Kantian ethicists find the proposal that people are citizens of some nonnatural world of reason implausible and unattractive. They aim to reconstruct the crucial elements of Kant's ethical theory without Kant's reliance on these metaphysical speculations. Most Kantian ethics are intended to develop Kantian ethical ideas while drawing on people's understanding of themselves as simply members of the natural world.
The strain in Kant's ethics that has found broadest employment is his idea that a practical principle (or "maxim") suitable for morally worthy action must be one which can hold universally, or, as Kant puts it, can be willed as a universal law; this is the first formulation of his "Categorical Imperative." Kant thought that when one acts immorally, one makes an exception of oneself, or makes exceptions for "just this one time," from laws one would will that everyone obey. Morality is thus best understood as the apprehension of principles that are universalizable in their scope and application.
This element of Kant's thought has echoes in numerous later thinkers. Marcus Singer (1961), for example, focuses on the general logic of what he calls the "generalization principle": What is right for one person must be right for anyone in the same or similar circumstances. One accepts the force of the question, "What would happen if everyone did that?" and Singer's theory is a study in the conditions of its legitimate application. Singer maintains that this principle is presupposed by any genuine moral judgment, and is the key to the moral principles that ground any plausible moral theory. However, Singer departs from Kant both in the metaphysical commitments previously described, and in his departure from considering what one could will to be universal, to assessing the desirability of the consequences of a principle with universal application.
Alan Gewirth's moral theory takes on the principle of generic consistency as its supreme moral principle. Like Kant, Gewirth (1978) begins with the premise that people are agents who act for ends; unlike Kant, Gewirth holds that, as agents, one must see the ends one is acting to realize as good. One sees them as good, however, only in light of certain properties, or "generic features," of those ends. For example, one might have the end of getting adequate nutrition in virtue of its natural role in healthy life and agency. But then, Gewirth argues, consistency requires that one sees anything else with those "generic features" as good as well; thus, to be consistent, one must see as good adequate nutrition for anyone. Moreover, people are committed to seeing as good not only their capacity for action but also the freedom and well-being that make it possible, and consistency requires that they see these as good for others as well. They must thus see themselves as having claims against others that they respect their "generic rights": rights to freedom and well-being. But the principle of universalizability requires that, if people see themselves as having claims against others, they must likewise see others as having the same claims against them. Thus, as in Kant, the bare idea of agency, coupled with the rational requirement of universalizability, leads to the fundamental moral principle, in this case the principle of generic consistency, "Act in accord with the generic rights of your recipients as well as of yourself" (Gewirth 1978, p. 135).
For many theorists drawing on elements of Kant's view (Singer is an example), the Kantian approach is attractive as a way to oppose consequentialism in ethics. However, not all consequentialists agree. R. M. Hare (1981) argues that the focus on universalizability can be taken to ground a form of consequentialism. Hare argues that Kant's insights into the logical properties of moral terms lead, not to Kant's own ethical conclusions, but to a form of utilitarianism. This is because people must recognize that moral principles are prescriptions of a certain sort, namely universal prescriptions. But such prescriptions are in turn best understood as a sort of preference, and when one considers one's preferences as being constrained by the requirement that they hold universally, one sees that one's prescriptions must take the familiar consequentialist form of maximizing utility.
Respect for Persons
The second formulation of Kant's categorical imperative stipulates that persons are not to treat other persons as means only, but always at the same time as ends. Kant is often thought to have identified something crucial to a proper understanding of morality in this principle, and this way of understanding our obligations of respect for other persons has been widely influential.
Alan Donagan's work begins with some of the essential elements recognized in the notion of universalizability, but develops them in a direction more congruent with this feature of Kant's theory. Donagan (1977) sees Kant as an exemplar of a moral theory based on a common core that reaches back to the Stoics, the Hebrews, and the Christian tradition. This core is based on the thought that morality is addressed to rational creatures as such, in virtue of their rationality, and that its precepts, or moral law, must somehow be accessible to moral agents in virtue of that rationality. In Donagan's view, what emerges from scrutiny of this common core is the requirement that every human being be treated with the respect due a rational creature. This is closely related to Kant's second formulation of the categorical imperative, which Donagan finds superior to the "universal law" formulation of that imperative. Thus Donagan is an example of a Kantian theorist who takes Kant's starting point in a shared capacity for rationality and ends with a focus on respect for human nature.
Others similarly have found this element of Kant's work central to their own ethical conceptions. Thomas Hill (1991) interprets the metaphysically hoary elements of Kant's theory as an examination of what it is for a deliberating agent to choose how to act, what ends to pursue, and so on. From this perspective, one's "autonomy"—one's capacity to see oneself as capable of more than simply the pursuit of self-interest or satisfaction of preferences—is crucial, as it presupposes that one's status as a rational agent must be essential in one's deliberating about how to act.
However, David Cummiskey (1996) argues that the focus on respect for persons as valuable in virtue of their status as rational agents can ground a consequentialist approach as well. Cummiskey maintains that Kant's attention to the value of persons as ends-in-themselves is appropriate, but is incapable of justifying the sorts of claims often made against consequentialist accounts, which by their nature require that value be maximized. Rather, Cummiskey argues, Kant's view that rational agents are ends in themselves is itself a view with a form of value at its core, and there is nothing in the balance of Kant's theory to block the inference that such value ought to be maximized as a matter of moral obligation.
Without question the greatest single influence in Kantian ethics has been the work of John Rawls (1971, 1999). Rawls's best-known work is in political theory, not ethics, and it draws more from Kant's method than from the content of Kant's views. Rawls took Kant's singular contribution to moral theory to be the notion that moral truth is not constituted independently of human reasoning and rationality—independent of individuals in such a way that moral truth can be treated as an object of investigation, as scientific truth is; instead, moral truth is something that instead people constitute or bring into being ("construct") through the very process of deliberating about it. In Kant's own theory, this idea is represented in the argument that people understand moral obligation by way of reflection on what principles could be willed as universal law. This approach brings to the foreground the procedures by which individuals deliberate about and attempt to determine fundamental moral principles. Rawls's political theory consists in large part of the characterization of such a procedure to arrive at principles of justice, which, he argues, are best understood not as something individuals discover, but as something they would arrive at on deliberation under certain carefully crafted conditions. The conditions Rawls specifies for this deliberation are also intended to capture important features of Kant's conception of what people are like as moral and political agents, in particular the distinction between individual persons, deserving of the sort of respect Rawls believes his theory of justice provides.
Rawls's influence can be seen not only in political theory, but in a resurgence of interest in Kantian foundations for moral and political theorizing generally. Christine Korsgaard (1996) has adapted the constructivist approach in developing her Kantian ethical theory. On her view people recognize that, as reasoning agents, they need reasons to act, and as they assess where such reasons can come from—as they consider possible "sources of normativity"—they realize in the end that they must come from their own rational natures. People take their reasons, Korsgaard argues, from their "identities," and fundamental to any and all of these identities is their moral identity—their identity as agents acting on reasons. Reasons, Korsgaard argues, are inherently public, in the sense that they must be shareable among agents, so the enterprise of reflecting on how to act itself gives rise to the principles governing one's conduct.
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Mark LeBar (2005)