This introductory study analyzes two key texts from the short-lived Argentine collective, the Asociación Arte Concreto-Invención (Association of Concrete Art-Invention, or AACI). Published in 1946 in the same issue of the group's official organ, they collectively theorize the “co-planar,” the AACI's key contribution to the history of abstract and concrete painting. While Maldonado's text offers a historical reconstruction of the genealogy of the co-planar as the culmination of modernist investigations of the plane and the problem of composition, Hlito's text outlines the understanding of Marxist materialism and dialectics that underpinned this particular take on the task of modernism.