From a theoretical point of view, most researchers agree that phraseological modifications are characterized by three key features: 1. occasionality, 2. intentional deviance from conventional use, and 3. context-boundedness. The present paper deals with the feature of occasionality and its operationalization in the context of text-based phraseological research. In text-based studies to date, occasionality has been identified with an absence of lexicographic codification. Phraseological structures and meanings registered in dictionaries have been regarded as conventional, uncodified structures and meanings, as occasional and, eventually, as modifications unless there is clear evidence of an unacceptable and incorrect use of the phraseme. In this paper, however, it is argued that a simple identification of lexicographic codification and conventionality on the one hand and non-codification and occasionality on the other does not permit an adequate distinction between conventional and occasional uses of phraseological units. Instead, in the approach proposed here, it is the relative frequency of the particular phraseological form in the DeReKo corpus (Deutsches Referenzkorpus) that is used as the distinctive criterion to decide upon its status as conventional or occasional.
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