This article provides a critical examination of the widespread idea that A and O (and Agents and Patients) are each other's mirror image in terms of case marking and semantic features. We examine patterns of differential case marking for nouns in a sample of 185 languages, showing that the behaviour of A cannot be captured in terms of markedness reversal based on models for O marking. We highlight pecularities of A marking that are not found with O marking, like sensitivity to the feature of motivity, and syntactic restrictions on use as A, and use these to develop an independent account of A marking.
Linguistic Typology publishes research on linguistic diversity and unity. It welcomes articles that report empirical findings about crosslinguistic variation, advance our understanding of the patterns of diversity, or refine typological methodology.