There is a review of a book titled "Rethinking Expertise" on PhysicsWorld website that I find rather interesting and appropriate. The author of the book makes a distinction between the level of expert knowledge that a person can have in reference to scientific knowledge. What is original here is the distinction between the highest level of expertise that allows one to make an original contribution, versus what the authors call "interactional expertise" where ".... people who have this kind of expertise share some of the tacit knowledge of the communities of practitioners while still not having the full set of skills that would allow them to make original contributions to the field...." I think that for most practicing scientists, we tend to know when we go from having a tacit knowledge and expertise of something (such as our area of study) to an area where we are, at best, having an interactional expertise. This is because we are aware of the level of knowledge and the amount of details that are needed to be an expert in a particular area. So we tend to know when we no longer have that. It then leaves 2 questions to ponder: 1. How many people are aware of the level of their knowledge in a certain area when they either offer an opinion, or engage in a discussion where tacit knowledge of something is required? 2. Is the level of expert knowledge not as strictly required in other areas outside of science? For example, in areas where "opinions" and how one sell one's ideas seem to matter more than the accuracy of the content (politics?), is there such a thing as the boundary between expert, interactional expert, and the pedestrian, average Joe? Zz.