Redundant morphological marking facilitates children's learning of a novel construction

The presence of redundant marking in languages raises interesting questions about the balance of different pressures in language learning and use. Speakers tend to avoid redundant elements in production: omitting (or reducing) more predictable elements. At the same time, languages maintain different types of redundant marking, such as encoding thematic assignment by both word order and case marking. Why is redundancy found in languages even though speakers seem to avoid it? Here, we propose that redundant cues can facilitate learning. We test this hypothesis in an artificial language learning study with children, where either word order alone or both word order and case marking serve as cues for thematic assignment in a novel construction. Results show that children learned the redundant language better despite having to learn an additional morpheme. We discuss implications for the effect of different cognitive pressures on language change.