The chapter delivers a biref description of Derrida's critique of the metaphisics of presence and shows its relevant implications for scientific inquiry. It is shown that the deconstruction of the concept of Being as a trascendental signifier is consistent with the scientific use of operational definitions that simplify the complexity of real world phenomena through the use of unrealistic assumptions. The argument reaches two main conclusions. First, the deconstruction of the trascendental signifier entails that unrealistic assuptions do not have a metaphysical status and they can change in accordance with the specific purposes of scientific inquiry. Second, the decostrustionistic framework implies that scientific analysis can asymptotically approximate the target phenomenon without reaching a full correspondence with it. These results are illustrated through the example of economic analysis of individual behaviour.