Most sciences use some forms of mathematics in the formulation of their theories. In this chapter I argue that our notion of scientific theories and scientific models should be kept apart. The argument is partly based on the distinction between what Saussure called “langue” and “parole” with respect to the natural language. Like this distinction I hold that a scientific theory corresponds to Saussure’s langue, providing the scientist with a vocabulary together with some implicit definitions and explicit rules of interpretation for how this vocabulary should be used. Hence, I deny that theories represent the world because mathematical equations as a system formally consist only of predicates and their relationships. In a model the scientist has introduced an idealized target system which he or she believes can be described by the predicates of the theory. The model enables the scientist to explain how things behave, and such statements may be either true or false. Hence statements generated from the model are what corresponds to Saussure’s parole. If true, such an analysis seems to deprive us from thinking that scientific theories may give us an exhaustive representation of humans in the world.