The article opens with a quote of three passages from a book concerning foreign language didactics that differ in their diction. It shows the differences between them to be significant: from the perspective of the prevaling sentence modality, the first and third passages are declarative, the second is desiderative, the first and second are theoretical while the third is metatheoretical. While veracity can be ascribed to declarative sentences, it is not so with desiderative sentences as they are valid only. This distinction has the following consequence: From the statement that something is, it cannot be inferred that something should be (the so-called Hume‘s law). The distinction between theory and metatheory is equally fundamental. The objects of theory are ontic, those of metatheory are semantic. The author comes to the conclusion that analogical distinctions in interpretations are valid for didactics in general.