Suppose that we develop a medically safe and affordable means of enhancing human intelligence. For concreteness, we shall assume that the technology is genetic engineering (either somatic or germ line), although the argument we will present does not depend on the technological implementation. For simplicity, we shall speak of enhancing “intelligence” or “cognitive capacity,” but we do not presuppose that intelligence is best conceived of as a unitary attribute. Our considerations could be applied to specific cognitive abilities such as verbal (...) fluency, memory, abstract reasoning, social intelligence, spatial cognition, numerical ability, or musical talent. It will emerge that the form of argument that we use can be applied much more generally to help assess other kinds of enhancement technologies as well as other kinds of reform. However, to give a detailed illustration of how the argument form works, we will focus on the prospect of cognitive enhancement. (shrink)