 The unidirectionality hypothesis is the idea that grammaticalization, the development of lexical elements into grammatical ones, or less grammatical into more grammatical, is the preferred direction of linguistic change and that a grammatical item is much less likely to move backwards rather than forwards on Hopper & Traugott's cline of grammaticalization.In the words of Bernd Heine, "grammaticalization is a unidirectional process, that is, it leads from less grammatical to more grammatical forms and constructions".That is one of the strongest claims about grammaticalization, and is often cited as one of its basic principles.