Constructing definitions as a goal of inquiry

In a class on perception, students, over the course of 3 weeks, constructed an account of "blurriness" with respect to vision, describing blurriness as occurring when "more than one ray from two separate points out in space are hitting the retina at one point." This account of blurriness, however, was just one of many introduced early on in our investigations of the eye. As students worked to model the eye and developed a consensus description of how lenses and pinholes create images, the "the separate points in space to one point on the retina" idea was refined, gained prominence in discussions and became a stable, useful, and precise concept. This paper explores one student's progressive understanding of blurriness, and the activities and interactions that supported the development of this definition.