  Physics Education Research (PER) applies a scientific approach to the
question, "How do our students think about and learn physics?" PER allows us to
explore such intellectually engaging questions as, "What does it mean to
understand something in physics?" and, "What skills and competencies do we want
our students to learn from our physics classes?" To address questions like
these, we need to do more than observe student difficulties and build
curricula. We need a theoretical framework -- a structure for talking about,
making sense of, and modeling how one thinks about, learns, and understands
physics. In this paper, I outline some aspects of the Resources Framework, a
structure that some of us are using to create a phenomenology of physics
learning that ties closely to modern developments in neuroscience, psychology,
and linguistics. As an example of how this framework gives new insights, I
discuss epistemological framing -- the role of students' perceptions of the
nature of the knowledge they are learning and what knowledge is appropriate to
bring to bear on a given task. I discuss how this foothold idea fits into our
theoretical framework, show some classroom data on how it plays out in the
classroom, and give some examples of how my awareness of the resources
framework influences my approach to teaching.
