The Author of the paper analyses the use of the word-formation-rules first of all in the grammar-book “Deutsche Grammatik” written by Helbig/Buscha (2001), where they exist on the edge of morphological rules. This principle can consider the word-formation-rules to be the complements of the morphological rules, when these have reached the boundaries of their use. The paper shows it on several examples. This principle corresponds also with the redaction of this grammar-book, that differentiates between main rules and their appendices.