leading from lexemes to grammatical formatives. A number of semantic, syntactic and phonological processes interact in the grammaticalization of morphemes and of whole constructions. A sign is grammaticalized to the extent that it is devoid of concrete lexical meaning and takes part in obligatory grammatical rules". Paul Hopper (1991): Hopper defined the five 'principles' by which you can detect grammaticalization while it is taking place: layering, divergence, specialization, persistence, and decategorization. František Lichtenberk (1991): In his article on "The Gradualness of Grammaticalization", he defined grammaticalization as "a historical process, a kind of change that has certain consequences for the morphosyntactic categories of a language and thus for the grammar of the language. James A. Matisoff (1991): Matisoff used the term 'metaphor' to describe grammaticalization when he wrote: "Grammatization may also be viewed as a subtype of metaphor (etymologically "carrying beyond"), our most general term for a meaning shift. [...] Grammaticalization is a metaphorical shift toward the abstract, "metaphor" being defined as an originally conscious or voluntary shift in a word's meaning because of some perceived similarity. Elizabeth Traugott & Bernd Heine (1991): Together, they edited a two-volume collection of papers from a 1988 conference organized by Talmy Givón under the title Approaches to Grammaticaliztion. They defined grammaticalization as "a linguistic process, both through time and synchronically, of organization of categories and of coding. The study of grammaticalization therefore highlights the tension between relatively unconstrained lexical expression and more constrained morphosyntactic coding, and points to relative indeterminacy in language and to the basic non-discreteness of categories". Olga Fischer & Anette Rosenbach (2000): In the introduction of their book Pathways of Change, a summary is given of recent approaches to grammaticalization. "The term 'grammaticalization' is today used in various ways. In a fairly loose sense, 'grammaticalized' often simply refers to the fact that a form or construction has become fixed and obligatory. (...) In a stricter sense, however, (...) the notion of 'grammaticalization' is first and foremost a diachronic process with certain typical mechanisms." Lyle Campbell lists proposed counterexamples in his article "What's wrong with grammaticalization?". In the same issue of Language Sciences, Richard D. Janda cites over 70 works critical of the unidirectionality hypothesis in his article "Beyond 'pathways' and 'unidirectionality'". A brief summary and review of the current state of research on the lexicalization/degrammaticalization sub-branch, including the most recent developments between 2000 and 2010, is provided by this paper on