In this article, we analyse the role performed by the principles in teaching scientific content. We observed that principles in the empirical sciences are generic heuristic guides in scientific production and by exercising this function, a principle is able to limit the feasible arbitrarinesses inside a theoretical system. In teaching, we have focused on the treatment of energy conservation principles in physics textbooks. We concluded that there is a fragile relationship between theory/model and objects/events in textbooks: consequently the treatment of principles only assumes a role as an additional technique to solve given problems. We suggested the enhanced treatment of principles in textbooks by bringing them closer to the theoretical function, so demanding, and motivating the students' creativity in constructing inferences limited by the validity of principles. That could happen through the presentation of non-modeled physical situations, neither idealized nor abstracted. Thus, heuristic wealth would be sought and not only the operational aspects.
principles; heuristic guides; conservation of energy principle; models