The Similarity Hypothesis in Metaethics

According to many contemporary philosophers practical normativity (what we ought to do) and theoretical normativity (what we ought to believe) must have the same metaphysical underpinnings. I refer to this as the Similarity Hypothesis. In this chapter I sketch the use of this hypothesis as a methodological assumption in contemporary metaethics and assess it. I focus on one argument against it. The argument is based on the claim that, whereas the attitude of belief may serve as the grounds of theoretical normativity, there is little prospect of an action-guiding attitude (e.g. desire or intention) serving as the grounds of practical normativity. I engage in detail with an argument from Stephen Darwall that might be thought to support this point and hence to undermine the Similarity Hypothesis.