Such a restricted view of social innovation is, of course, not what the authors intend. They offer additional resolution in their definition of social value: “The creation of benefits or reductions of costs for society—through efforts to address societal needs and problems—in ways that go beyond the private gains and general benefits of market activity.” The operative concept here, and the real differentiation from Barro’s view, is the reference to benefits that “go beyond … market activity.” This phrase directs us to the Achilles’ heel of Barro’s otherwise seemingly solid analysis. Barro knows that markets for many goods are imperfect or nonexistent. As a consequence of incomplete markets, the value of trade between two individuals in many cases will not reflect impacts on third parties. Such impacts are termed “externalities” by economists, capturing the idea that significant costs or benefits of a transaction are “external” to the parties directly involved in making the deal.