Meillet以后的欧美学者给出了许多语法化定义,其中以Hopper和Traugott的定义最为经典。单向性是语法化理论最激进的假设,去范畴化、斜坡和主观化是单向性的重要表现。 Meillet later European and American scholars have given many grammatical definitions, of which Hopper and Traugott are the most classic definition. Unilateralism is the most radical assumption of grammaticalization theory. Categorization, slope and subjectification are important unidirectional manifestations.