It is commonly assumed that patterns of syncretism in inflectional paradigms are restricted in some way. In this article, I show how such restrictions can reflect cognitive constraints on language learning. Namely, I construct a learning algorithm that is biased toward certain types of affix distributions in paradigms, thereby rendering them systematic. In developing this algorithm, I rely on the traditional notions of underspecification and blocking , but recast them in terms of learners' biases toward generalization strategies based on cross-situational intersections and default reasoning. This algorithm allows us to test claims about systematicity of syncretism using typological data and language acquisition studies. In the last part of the article, I present a crosslinguistic survey of verbal agreement paradigms that supports the algorithm's predictions.