The Unique Vector Constraint: The Impact of Direction Changes on the Linguistic Segmentation of Motion Events

This chapter explores a principle of motion event coding that appears to be shared across languages: the unique vector constraint (UVC). The UVC determines the complexity of direction information that can be coded in simple motion event clauses. According to the UVC, all direction specifications in a single simple clause must denote the same direction vector. The UVC differs from another principle of motion event coding, the argument uniqueness constraint (AUC), which requires the unique assignment of path roles such as 'source', 'via', 'goal', 'toward', etc. in single simple clauses. It is argued that both constraints are principles of form-tomeaning mapping at the syntax-semantics interface.