In his paper "The Influence of Normative Reasons on the Formation of Legal Concepts", German legal philosopher Lorenz Kähler offers a very interesting approach to normativity for the Russian theory and philosophy of law. L. Kähler, considering various normative reasons that influence on the formation of legal concepts, puts forward original and sometimes unexpected conclusions. On the one hand, this can be attributed to the peculiarities of his writing style, but on the other hand, it sometimes seems that he deliberately provokes the reader to questions, involving him in a discussion. In L. Kähler’s approach, there are at least two arguments that require serious clarification and discussion. First, the fact that all the concepts used in legal norms are legal, and, secondly, that the legislator can use lexical, stipulative and real definitions to disclose a content of these concepts. The counterarguments and criticisms offered in this article are based on the statements that the definition is one of the ways of forming legal concepts, and that the question of what is meant by concepts is closely related to the question of which definitions the legislator can use. This led to the following conclusions. First, that in the formulation of legal norms, non-legal concepts, legal concepts and concepts of the law can be used, and this use does not entail that all these concepts become legal. Second, that three types of definitions (lexical, stipulative, and real) are clearly not enough to define these concepts. Moreover, not all of these definitions can be effective and productive, and only some of them are normative in nature. Therefore, it is necessary either to expand the list of definitions, or to significantly modify them in accordance with the specifics of the field of application.