This study illustrates the origin and the grammaticalization path of 若 based on its occurrences in the Oracle-Bone Inscriptions (OBI in short), The Book of Documents, The Book of Odes, The Analects, and Mencius. 若 in the OBI means ‘to follow,’ ‘to allow,’ or ‘to be in accord with.’ In The Analects and Mencius, 若 as a verb means ‘to resemble’ or ‘to be like.’ It also expresses a simile. It is used in the form [A+不/弗/莫+若+B] or [A+豈若+B] meaning that A is inferior to B. From a verb meaning ‘to resemble’ or ‘to be like,’ 若 is further grammaticalized into a topic marker and a conditional marker. These topic and conditional markers share syntactic and semantic similarities. Syntactically, both of them appear in the form [若+NP/VP, (則)+VP]. Semantically, they provide the framework for the following discourse. It is very common cross-linguistically that a topic marker is also used as a conditional marker. Examples include 要說 and 的話 in modern Chinese. 若 is also used as a demonstrative adverb and a demonstrative adjective. It is one of the *N- demonstratives that appeared in Archaic Chinese, which later developed into the second-person pronouns. Whether 若 as a demonstrative means proximate or distal awaits a further study.