I present clear evidence from Karimata-Miyako Ryukyuan that semantic change can precede a syntactic change in the process of grammaticalization. In this dialect, the morpheme ufu has an aspectual and a conjectural use, and the change proceeds from the former to the latter in accordance with the “scope-increase” (Tabor & Traugott 1998) hypothesis. While the aspectual use of ufu only takes accomplishment and activity verbs, carrying their resultative interpretations, the conjectural use is insensitive to the aspectual type of verbs and is also compatible with achievement and state verbs. In addition to evidential/modal meanings, ufu develops a tense-like meaning that refers to the past. In spite of those semantic developments, ufu occupies the same syntactic position as that of the aspectual use.