In this clip, you hear a back-and-forth between Deputy Solicitor General Stewart and Justice Scalia regarding the necessity of EPA’s being able to take costs into account—which industry challengers argue is prohibited by the statute—in carrying out the good neighbor provision of the Clean Air Act. Industry challengers argue that a cost-based approach is unfair to upwind states that have relatively minor emissions problems but end up paying more, whereas the EPA argues that given the variety of factors that create a “significant” contribution, a straight proportionality calculation is impossible and that an efficient solution must include consideration of cost. You hear Mr. Stewart discuss why a proportionality calculation based on amount of pollutants is unworkable, pushback from Justice Scalia, and a response by Mr. Stewart about the illogic of the industry challengers’ argument: “[T]he only ill consequence of overcontrol is cost. … The only reason that people worry about overcontrol, about reducing emissions more than they need to be, is that it costs money. And if that’s the problem to be avoided, it seems strange that EPA can’t take account of costs in devising a solution.”