ABSTRACT: In his search for a better scientific language, Carnap offered a number of definitions, ideas, and arguments. This paper is devoted to one of his definitions in this regard. In particular, it addresses a definition providing rules to add new properties to the descriptions of objects or beings by taking into account other properties of those very objects or beings that are already known. The main point that this paper tries to make is that, if a current cognitive theory such as the theory of mental models is assumed, it can be said that those rules are easy to use by scientists and philosophers of science. This is because, following the essential theses of this last theory, the rules do not demand excessive cognitive effort to be applied. On the contrary, they are simple rules that make researchers’ work harder in no way.