The term "sprachlicher Zweifelsfall" ('linguistic case of doubt') is not yet well established in the terminology of linguistics. The first part of the paper therefore outlines a definition of "sprachlicher Zweifelsfall" and a classification of various types. Basically, the definition takes up the fact that even fully competent speakers sometimes do not know definitely which variant to choose from two (or more) alternatives. Doubts like this evolve on all levels of language (phonetics, morphology, lexic, syntax, semantics). Considering the emergence of "Zweifelsfälle", it is argued that they arise mainly from the existence of written language and more or less standardized varieties of language. At least some of their features refer to the specific conceptual conditions of writing and reading. In the second part of the paper, the "Zweifelsfälle" are reconceived in so far as they have been treated in the newer history of German discourse on language, including both popular and philological discussion. Starting in 19th century thought, they became symbolic means of social distinction. In contrast, linguists tended to neglect the existence of "Zweifelsfälle" because they did not fit in well with their theories on language. The paper ends with several theses dealing with possible future research on the topic.