Kant's Search for the Supreme Principle of Morality (review)

Summed up in a sentence, this book is both a critical examination of Kant's claim to have derived a supreme moral principle and a limited defense of Kant's project that appears to depart significantly from Kant's own approach. Methodologically, a large portion of this book is devoted to analyzing various key concepts and claims about the nature of the categorical imperative in the Groundwork of the Metaphysics of Morals and the Critique of Practical Reason and testing them against "everyday" moral intuitions via numerous examples and counterexamples.

Kerstein begins by distinguishing between the tasks of deduction and derivation of a supreme moral principle, whereby a deduction is understood as an argument for the existence of a supreme moral principle, and a derivation simply assumes this conditionally and goes on to argue that a particular principle and no other can claim the title. Kerstein waives the discussion of whether Kant succeeds in giving a deduction and hence satisfactorily refutes moral skepticism. His focus in the book is on the derivation proposed primarily in Groundwork I and II that if there is a supreme moral principle, then it must be that law expressed in his formulations of the Categorical Imperative (hereafter "CI"). Kerstein addresses Bruce Aune's "traditional" reading of Kant's derivation, wherein the argument utterly fails because Kant allegedly infers a relatively substantive command ("Act only on that maxim which you can at the same time will to be universal law") from a purely formal, higher order, and hence relatively empty one ("Conform your actions to universal law"). He then devotes a chapter each to two recent, influential defenses of Kant's derivation that seek his argument outside the Groundwork. Kerstein addresses Henry Allison's attempt to rescue the derivation via an account of agency rooted in Kant's notion of transcendental freedom, elaborated in the second Critique. Kerstein rejects Allison's reconstruction on the grounds that it remains too abstract to generate the degree of specificity arrived at in Kant's Groundwork universalization formulation. Chapter Three examines Christine Korsgaard's alternative reconstruction of Kant's argument that focuses on the formulation of humanity ("Act so as to treat humanity, whether in your own person or that of any other, always as an end and never as a means only"). He rejects her interpretation because, again, the move from the abstract command to conform to universal law to the substantive formulation about humanity as a universally recognizable unconditional good fails. From the former, more abstract claim, he argues, it does not follow that there is a universally recognizable unconditional good, let alone that this good is humanity in itself (and not, say, utility [happiness], or even some intrinsic value unrelated to humanity, both of which Kant rejects as candidates for the unconditionally good).

In his own reconstruction, Kerstein dissolves the criticism of the traditional reading of Kant's Groundwork derivation of the formula of universal law by simply denying that Kant argues directly from the more generic principle to the specific versions of the CI (91ff). Instead he suggests that Kant's argument is less direct, made by way of laying out a set of criteria that any supreme principle must meet, and showing how the CI meets them while no other candidates can. In the second half of the book he takes a painstaking and critical look at a total of eight criteria, each of which Kant holds to be necessary and together are jointly sufficient for establishing the CI as "the supreme norm for the evaluation of the moral permissability and requiredness of an action, but not of its moral value" (165). This statement includes Kerstein's most controversial and interesting reconstructive claim, namely his denial that moral worth attaches only to actions done in accordance with duty as determined by the test...