  In this paper, we describe two paradigms in physics education research (PER):
recurrence-oriented and case-oriented PER. We connect theory on research
methodologies in the social sciences to interviews with physics education
researchers and examples of published PER to articulate the specific
assumptions of recurrence- and case-oriented PER. We show that the different
assumptions made in these two paradigms bear out in specific aims and research
designs taken up by physics education researchers. In particular,
recurrence-oriented research seeks reproducible, representative patterns and
relationships; human behavior is modeled as governed by lawful (albeit
probabilistic) relationships. Case-oriented research, in contrast, seeks to
refine and develop theory by linking that theory to cases; human action is
assumed to be shaped by the meanings that participants make of their local
environments. We briefly offer examples in which researchers take up both the
recurrence- and case-oriented research paradigms.
