This paper discusses the issue of how coordinate structures evolve into subordinate structures in both syntactic and semantic terms. I call this type of process "conjunctive reduction." It is well established in the literature on Chinese historical syntax that some modifier-head and verb-complement compounds actually derive from coordinate structures in Ancient Chinese. Based on this finding, I suggest that a similar process is also at work in Formosan languages, but on a quite different scale. That is, while Chinese encodes conjunctive reduction in compounding morphology, the same process involves full-fledged syntactic operations in Formosan languages. I propose that there are two general directions of conjunctive reduction. On the one hand, the coordinator may become a modifier marker, where the first conjunct becomes a marked adverbial; then the modifier marker may disappear completely, making the first conjunct an unmarked adverbial. I call this "adverbialization." On the other hand, the coordinator may become a complementizer, introducing either an infinitive complement or an adverbial adjunct such as a conditional or temporal clause. I take Squliq Atayal, Tsou, and Amis to represent the Northern, Tsouic, and Paiwanic groups respectively, which in turn points to the existence of a protolanguage with extensive coordinate construals along the line of Neo-Davidsonian semantics, very much like Ancient Chinese.