 the predominant measure of just compensation should be "market value." As Justice Frankfurter reasoned in Kimball Laundry Co. V. United States: "Most things have a general demand which gives them a value transferable from one owner to another. As opposed to such personal and variant standards as value to the particular owner whose property has been taken, this transferable value has an external validity which makes it a fair measure of [just compensation]" (338 U.S. 1, 5 (1949)).2 23 The external validity identified by Justice Frankfurter has both a theoretical and a practical basis. As a theoretical matter, market value reflects the seminal economic insights that effectively transformed value from the intrinsic concept of a good to the result of market transactions between buyers and sellers. A good's market value provides observable evidence a market price of the benefits to buyers and the costs to sellers. Market value thus sheds light on property rights by considering the returns in transferring those rights. In evaluating the value of assets used in production, market value provides tangible evidence of the property's earning potential. This shift was evident in Monongahela Navigation Co. V. United States, the first case in which the Court addressed just compensation principles. The Court determined that the Takings Clause required compensation not only for the tangible property taken, a lock and a dam, but also for the tolls the facility would have earned by using that property. The Takings Clause required payment of "a full and perfect equivalent for the property taken," which, "generally speaking, is determined by its productiveness, the profits which its use brings to the owner." "The value, therefore, is not determined by the mere cost of construction, but more by what the completed structure brings in the way of earnings to its owner." As a result, the income that the lock and the dam would have earned was considered part of the property's value Co. V. United States, 187 F.3d 1324, 1338 (11th Cir. 199