There are therefore four times more catenae in the tree than there are constituents. The inclusivity and flexibility of the catena unit becomes apparent. The following Venn diagram provides an overview of how the four units relate to each other:  The catena concept has been present in linguistics for a few decades. In the 1970s, the German dependency grammarian Jürgen Kunze called the unit a "Teilbaum" 'subtree'. In the early 1990s, the psycholinguists Martin Pickering and Guy Barry acknowledged the catena unit, calling it a "dependency constituent". However, the catena concept did not generate much interest among linguists until William O'Grady observed in his 1998 article that the words that form idioms are stored as catenae in the lexicon. O'Grady called the relevant syntactic unit a "chain", however, not a "catena". The term "catena" was introduced later by Timothy Osborne and colleagues as a means of avoiding confusion with the preexisting chain concept of Minimalist theory. Since that time, the catena concept has been developed beyond O'Grady's analysis of idioms to serve as the basis for the analysis of a number central phenomena in the syntax of natural languages (e.g. ellipsis and predicate-argument structures). Idiosyncratic language of all sorts can be captured in terms of catenae. When meaning is constructed in such a manner that does not allow one to acknowledge meaning chunks as constituents, the catena is involved. The meaning bearing units are catenae, not constituents. This situation is illustrated here in terms of various collocations and proper idioms. Simple collocations (i.e. the co-occurrence of certain words) demonstrate well the catena concept. The idiosyncratic nature of particle verb collocations provide the first group of examples: "take after", "take in", "take on", "take over", "take up", etc. In its purest form, the verb "take" means 'seize, grab, possess'. In these collocations with the various particles, however, the meaning of "take" shifts significantly each time depending on the particle. The particle and "take" convey a distinct meaning together, whereby this distinct meaning cannot be understood as a straightforward combination of the meaning of "take" alone and the meaning of the preposition alone. In such cases, one says that the meaning is "non-compositional".