Abstract
We study the acquisition of case by two young Viennese children, a boy and a girl according to their longitudinal corpora of output and maternal input. In critical discussion of previous psycholinguistic literature and of various theoretical approaches the analysis supports the insistence of Natural Morphology on markedness hierarchies, universal preferences (especially transparency, salience as an expression of figure-ground contrast and optimal size on the posiive side, little iconicity and much ambiguity as negative factors), typological adequacy, productivity as a property of system adequacy. Interindividual differences in their development are explained by the boy being a segmental child, the girl rather a prosodic child.