In this article I will compare two approaches for defining theoretical terms, that of Logical Empirism and that of Structuralism. I will determine explicitly the accounts of theoreticity in both Logical Empirism and Structuralism, and compare them by means of a case study: a structuralistic reconstruction of Neurobiological Constructivism. I will point out that the structuralistic criticism on the account of theoreticity of Logical Empirism is insufficient and that the structuralistic criterion of theoreticity does not satisfy the requirements of demarcation (...) for theoretical terms demanded by Logical Empirism. (shrink)