For a long time proponents of the conceptual view were so keen on proving that conceptual metaphors and metonymies exist that they mainly concentrated on compiling extensive lists of conceptual mappings and their corresponding linguistic instantiations. Their status as conventional units was, however, usually taken for granted and hardly ever explicitly addressed, let alone called into question. Often researchers neither paid attention to how frequently the different mappings are really exploited in natural discourse nor discussed the question whether all potential linguistic instantiations of a given mapping are equally accepted by the speech community. This is a serious shortcoming since there is considerable synchronic variation with respect to both the overall productivity of different conceptual mappings and the speech community's acceptance of figurative senses which are based on one and the same mapping.
Recent years have witnessed more differentiated approaches to the issue of conventionality: Especially with regard to metaphors researchers have tried to come to terms with it by means of usage-based studies (e.g. Hanks 2006, Stefanowitsch 2006, Svanlund 2007). For metonymy, however, such studies are still scarce so that most of the few sources which tackle the question as to how conventional single metonymic mappings and their linguistic instantiations are, are purely theoretical.
Therefore, I will focus on the field of metonymies and first briefly review two types of theoretical models: the prototype-based views of Peirsman and Geeraerts (2006), and of Barcelona (2002, 2003, 2004), and a relevance-theoretical approach by Papafragou (1996). The predictions of these models will then be compared to the results of a large-scale corpus study. It will be shown that both types of models are too crude to account for all the findings: The prototype-based ones cannot cope with the fact that far from all linguistic metonyms motivated by one mapping are homogeneous in terms of their frequencies. The relevance-theoretical model explicitly allows this, but cannot explain why some interpretive uses are later accepted as descriptive content whereas others are not.
However, a comprehensive account of the conventionality of metonymies should be able to answer all of the following questions: First, which positions do different metonymic mappings of different degrees of generality occupy on the continuum of conventionality? Second, which positions on this continuum can be assigned to different linguistic instantiations? And third, and perhaps most importantly, which factors are responsible for the different degrees of conventionality on the conceptual and the linguistic level? While the first and second question can be answered by extensive corpus studies, which help determine the frequency of mappings and linguistic realizations, the third calls for methods which mirror conceptual structure and cognitive preferences in a more direct way. The key to the various degrees of conventionality on both levels, it will be argued, is salience: Ontological salience (cf. e.g. Langacker 1993, Radden and Kövecses 1999) determines, at least on an intermediate level of generality, the conventionality of different metonymic mappings. And the relationship between the overall conventionality of a mapping and the actual conventionality of single linguistic instances is governed by the salience of target-related attributes in the vehicle concept. A full account of the conventionality of metonymies thus presupposes a combination of different methods. Neither corpus-linguistic nor psycholinguistic approaches alone can reveal and explain all the factors involved in the complex issue of conventionality.
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Peirsman, Yves and Dirk Geeraerts (2006), "Metonymy as a prototypical category", Cognitive Linguistics 17(3), 269-316.
Radden, Günter and Zoltán Kövecses (1999), "Towards a theory of metonymy", in Klaus-Uwe Panther and Günter Radden, eds., Metonymy in language and thought, Amsterdam – Philadelphia: John Benjamins, 17-59.
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Stefanowitsch, Anatol and Stefan Th. Gries, eds. (2006), Corpus-based approaches to metaphor and metonymy, Berlin – New York: Mouton de Gruyter.