J. B. Schneewind's Sidgwick's Ethics and Victorian Moral Philosophy surpassed all previous treatments of Sidgwick's The Methods of Ethics by showing how Sidgwick's work follows a coherent plan of argument for a conception of ethics as grounded in practical reason. Schneewind offered his interpretation as the product of a historical rather than a critical study. This article undertakes a critical study of Sidgwick's work based on Schneewind's interpretation. Its thesis is that the conception of ethics for which Sidgwick argued is incoherent. As a result, it is argued, the coherent plan of argument in the Methods that Schneewind disclosed masks a deep incoherence in the argument itself.