One formative idea behind the workshop on expertise in Berkeley in August of 2010 was to develop a viable "trading zone" of ideas, which is defined as a location "in which communities with a deep problem of communication manage to communicate" (Collins et al. 2010, p. 8). In the current case, the goal is to have a trading zone between philosophers, sociologists, and psychologists who communicate their ideas on expertise such that productive interdisciplinary collaboration results. In this paper, I review Harry Collins' three-dimensional model of expertise and provide a very brief and non-inclusive overview of a psychological response. In addition, I propose an addendum to the model by adding a fourth—natural talent—dimension.