Economic valuation is often deemed an important source of information for land-use policy. Stated preference methods (SPM) are a particularly potent class of economic valuation methods, but they are also particularly controversial. In response to accumulating criticism of SPM, deliberative monetary valuation (DMV) has been proposed as an alternative approach. DMV has gained considerable attention in recent years—however, being a combination of elements from neoclassical economic theory and from the theory of deliberative democracy, it lacks a consistent theoretical foundation, especially regarding rationality assumptions. In our paper, we aim at closing this gap and propose to found DMV on Amartya Sen’s approach to rationality. We show that his approach fits well the motivation for engaging with DMV and discuss its implications for the practice of DMV.