This article deals with the concept 'particle', specifically with the German notion of 'Abtönungspartikel'. These pragmatic or modal particles were first discussed in contemporary German grammars by Harald Weydt. Although the concept itself is clear, it is difficult to include such a category in existing grammars, as is shown by the treatment of such inflexible words in different editions of the standard German grammar, Der Duden. It seems difficult to formulate a description of the word class 'particle' in such a way that it includes pragmatic particles as well as other kinds of particles, such as focus particles. This problem is not new, and I also discuss parallels from the history of linguistics.