The book is the first in-depth study that aims to identify the conceptual rules and regularities underlying the (un)conventionality of figurative ways of speaking and reasoning. Using a combination of corpus-linguistic and cognitive-linguistic methods it investigates a large number of metonymies as well as metaphors, focusing on the former, less studied phenomenon. It provides an overview of their relative frequencies of occurrence in natural discourse and offers a systematic account of why some figurative expressions and/or conceptual mappings are preferred while others are less successful in the speech community and thus shape our language and thought to a lesser degree. Based on a critical examination of existing theories and material from the British National Corpus, the book points out similarities and differences between metonymy and metaphor as well as between different types of the two phenomena with regard to their conventionality and moreover demonstrates the value of usage-based studies for the cognitive-linguistic enterprise.