The basic idea is simple enough. Consider a familiar tool or artifact, say a pair of scissors.2 Such an artifact typically exhibits a kind of double adaptation - a two-way fit, both to the user and to the task. On the one hand, the shape of the scissors is remarkably well fitted to the form and the manipulative capacities of the human hand. On the other hand (so to speak), the artifact, when it is in use, confers on the agent some characteristic powers or capacities which humans do not naturally possess: the ability to make neat straight cuts in certain papers and fabrics, the ability to open bubble packs, and so forth. This is obvious enough; why else would we value the artifact at all?