nafs al-markab) is translated as "in the same boat," and it carries the same figurative meaning as the equivalent idiom in English. According to the German linguist Elizabeth Piirainen, the idiom "to get on one's nerves" has the same figurative meaning in 57 European languages. She also says that the phrase "to shed crocodile tears," meaning to express insincere sorrow, is similarly widespread in European languages but is also used in Arabic, Swahili, Persian, Chinese, Mongolian, and several others. The origin of cross-language idioms is uncertain. One theory is that cross-language idioms are a language contact phenomenon, resulting from a word-for-word translation called a calque. Piirainen says that may happen as a result of lingua franca usage in which speakers incorporate expressions from their own native tongue, which exposes them to speakers of other languages. Other theories suggest they come from a shared ancestor language or that humans are naturally predisposed to develop certain metaphors. Dealing with non-compositionality The non-compositionality of meaning of idioms challenges theories of syntax. The fixed words of many idioms do not qualify as constituents in any sense. For example: The fixed words of this idiom (in bold) do not form a constituent in any theory's analysis of syntactic structure because the object of the preposition (here this situation) is not part of the idiom (but rather it is an argument of the idiom). One can know that it is not part of the idiom because it is variable; for example, How do we get to the bottom of this situation / the claim / the phenomenon / her statement / etc. What this means is that theories of syntax that take the constituent to be the fundamental unit of syntactic analysis are challenged. The manner in which units of meaning are assigned to units of syntax remains unclear. This problem has motivated a tremendous amount of discussion and debate in linguistics circles and it is a primary motivator behind the Construction Grammar framework. A relatively recent development in the syntactic analysis of idioms departs from a constituent-based account of syntactic structure, preferring instead the catena-based account. The catena unit was introduced to linguistics by William O'Grady in 1998. Any word or any combination of words that are linked together by dependencies qualifies as a catena. The words constituting idioms are stored as catenae in the lexicon, and as such, they are concrete units of syntax.