Journal of the History of Philosophy

Brian Leiter’s second book on Nietzsche brings together ideas and arguments that have already had a significant influence on the field through their earlier formulations in his articles from the past two decades. It is thus indispensable reading for anyone interested in Leiter’s evolving project of showing that Nietzsche has the correct naturalistic approach to issues in moral philosophy and moral psychology. As usual with Leiter’s scholarship, this monograph is extremely clear, densely argued, and philosophically sophisticated.

Leiter nicely frames this book with an introduction in which he offers his latest thoughts on Nietzsche’s naturalistic approach and with a concluding chapter in which he joins Joshua Knobe to make a strong argument that contemporary human sciences favor Nietzsche’s picture of human moral psychology over those offered by the rival Aristotelian and Kantian traditions. In between, Leiter divides his book into two parts where he revisits his first book’s discussions about Nietzsche’s arguments against moral realism (part 1) and against free will (part 2). Here, however, he adds a lot of compelling new material that takes into account the intervening explosion of interest in Nietzsche’s philosophical psychology. Due to length restrictions, I will just raise a few questions about Leiter’s central claim that Nietzsche’s naturalistic approach leads him to be “an anti-realist about value, including his own” (65).

As in his first book, Leiter argues for a “methodological” interpretation of Nietzsche’s philosophical naturalism, meaning that Nietzsche thinks his positions “must answer to the facts as they unfold in the course of systematic empirical inquiry” (9). But here he broaches an important criticism of this interpretation: “Nietzsche seems to have been right about much of human moral psychology notwithstanding his failure to employ any of the methods of the empirical psychology that has confirmed much of his work. What kind of methodological naturalism is that?” (10, Leiter’s emphasis). In response, Leiter reiterates his claim that Nietzsche was a “speculative” methodological naturalist, as he had to be, “given the primitive state of psychology in the nineteenth century” (5). What this means is that Nietzsche’s “genius” showed him how to use unsystematic data and methods—that is, the psychological observations gleaned by himself and other discerning historical figures, as well as his study of contemporaneous psychological research—so as to arrive at hypotheses that are now vindicated by empirical findings and experimental methods in personality and social psychology, cognitive science, neuroscience, and behavioral genetics (9–11, 82–83, 166).

What is worrying about this response is that Leiter’s black box appeal to Nietzsche’s speculative genius does not seem to be either naturalistic or methodological. Indeed, we usually take it for granted that genius is not replicable. So a better option might be to look somewhere less anachronistic and more exegetically grounded for Nietzsche’s understanding of philosophical naturalism. Section 109 of The Gay Science seems a plausible choice, because here Nietzsche explicitly proposes a replicable methodological program that does not depend on his own genius and does not have to await confirmation by [End Page 160] future science. The goal, he says, is to purify our conception of nature of any falsifying anthropomorphic admixture—including especially all values—and then to translate our human psychology back into this purified conception (see also KSA 9:11[211]).

I think this suggestion, that Nietzsche proposed a systematic correction of the enormous “projective error” involved in value realism (29), is a better interpretation of his argument against moral realism than the one offered by Leiter. In a shift from his first book, Leiter now claims that this is not so much an argument from disagreement in moral attitudes but rather from the intractable disagreement recorded throughout the history of moral philosophy (29–30). According to Leiter, Nietzsche thinks that the best (i.e. naturalistic) explanation for this disagreement (23) appeals to natural facts about human beings (i.e. psycho-physiological and social facts) and does not need to make any reference...