The purpose of this paper is firstly to bring to light cases of rivalry, complementarity and cooperation between German prepositions and prepositions, prepositions and morphologically-related adverbs, prepositions and verb-particles. Secondly, it tries to show a) that "abstract prepositions are not semantically empty and cannot be reduced to mere syntactic functions; b) that this semantic content has nothing to do with valency (be it that of nouns, verbs or adjectives); c) that their meaning does not depend on whether they are used in idioms or not.