Underdetermination, associated with the Duhem--Quine thesis, is a familiar if under-researched theme in economics. In the light of this, we examine the development of urban land and housing economics. Through its Cartesian dualistic delineation of theory and data, the contemporary mainstream approach appears unable to circumvent the problem of underdetermination. In effect, it employs the strong version of Duhem--Quine in its retention of the assumption of a single, unitary competitive market (and associated access--space trade-off). Conversely, we highlight the affinity of Ely's (and the later Columbia School's) approach to pragmatists Dewey and Peirce, which provides a more fruitful basis for explanation. Copyright 2006, Oxford University Press.