Didactic science, like all sciences, has limits. It cannot tell teachers what they should teach, with what means, nor can it tell them what they should teach for. Nevertheless, didactics has an enormous transforming power. It can provide us with well-founded criteria for choosing the most appropriate means in order to achieve certain previously determined educational goal. And it can tell us what consequences (intended or unintended) will be obtained if certain didactic means are used. In short, it can evaluate the functioning of the current mode of study in an educational institution, explain its possible inconsistencies and study the viability of certain changes.