Abstract In the Jieyang Southern Min dialect, the negative 無 bo55 has evolved into a conjunctive that is used in multiple constructions: negative conditionals, cause and effect, disjunctives, and proposals. This paper aims to describe the multiple functions of 無 bo55 and to construct its grammaticalization path as compared with those of 否則 fouze ‘otherwise or else’, and 要不 yaobu ‘if not’, in Mandarin. It is common in Chinese and other languages for a negative to combine with its adjacent conjunctive to develop a new conjunctive. However, the Jieyang dialect exhibits a unique feature in that 無 bo55 is grammaticalized into a conjunctive per se by applying a complicated process of reasoning involving the logical relations among clauses without the support of any conjunctive constituents. This phenomenon can provide a new model for the study of grammatical evolution.