This paper investigates and defines the relationship between comitative and phrasal conjunction structures in Mandarin Chinese, with a view to determine the directionality of derivation between the two. Phrasal conjunction as discussed in previous works is examined under situational, lexical, and logical constraints, and it is shown here that phrasal conjunction associated with lexical constraint is but a surface structure phenomenon. ‘Principality’ is observed to underlie comitative constructions, which distinguishes the two otherwise closely related structures. With the clarification and establishment of the ‘unidirectional’ structure, which together with the comitative structure constitutes ‘association’ constructions, the conclusion that comitative is derived from phrasal conjunction is reached. Implications in English are also discussed.