Ritter and Harley (1998) have proposed that morphological features are organized in a feature geometry, and that this explains both the observed regularities, and the possible variations. Our assumption that this geometry is provided by Universal Grammar makes strong predictions about the acquisition of personal pronouns. In the first part of this paper, we discuss acquisition facts which not only provide independent support for this geometry, but additionally motivate universal defaults for major organizing nodes, specifically 1st person for [Participant] and 3rd person, singular for [Individuation]. In the second part of the paper we explore the consequences of the postulation of universal defaults by investigating relatively complex person systems.