Some bioethicists have argued in favor of a sliding scale notion of competence, paternalistically requiring greater competence in relation to more significant risk. I argue against a sliding scale notion, taking issue with the positions of Allen E. Buchanan and Dan W. Brock, Ian Wilkes, and Joel Feinberg. Rejecting arguments that a sliding scale is supported by legal cases, by ordinary usage, and by fallible judgments about competence, I argue in favor of greater evidence of competence when risk is greater. Two clinical cases are examined, both involving amputation, to show that my fixed concept of competence, with a requirement of clearer evidence of competence when risk is high, better accounts for good moral decisions in bioethics.