Richard A. Posner. Sex and Reason. Cambridge: Harvard University Press, 1992. Pp. vii, 458. $29.95.

With his special gift for contrariety, Judge Richard Posner places his ambitious investigation of the vicissitudes of sex under the aegis of a quote from Aristotle's Nicomachean Ethics: "Pleasures are an impediment to rational deliberation, and the more so the more pleasurable they are, such as the pleasures of sex - it is impossible to think about anything while absorbed in them." Posner then devotes the ensuing 442 dense pages to challenging Aristotle's assertion. That sex and reason normally make incompatible bedfellows should not be taken as evidence that it is impossible to subject sex to the rigors of reason. Sex, Posner suggests throughout the book, must be considered as one form of behavior among many, no more nor less immune to the operations of the rational mind.

Posner's commitment to the power of rationality, as he understands it, constitutes the great strength and ultimate weakness of his work. And it is easy to imagine that many readers will find his rational foray into sex infuriating. He has no patience for the facile confusion of sex with passion, much less of sex with desire, which so mesmerizes contemporary critics. Posner's discussion of sex has more to do with theories of animal behavior than with the feelings of individuals. In this respect the great strength of Posner's book overlaps with its most disturbing weakness, namely, his determination to organize complex human behavior in predictable- and largely determined-patterns.