Mark and Seth build on parts 1 and 2 of our discussion of Marcus to get further into the specifics of his metaphysics and how this is supposed to relate to behavior. Can Stoic directives really come solely "from reason," as he claims? How does this interact with the behaviors that we pursue (appropriately, according to Marcus) "by nature," i.e., without conscious deliberation required? Seth is concerned with how individualistic the philosophy is. Mark is concerned that if you discard the metaphysics (as modern skeptics largely do), why should you expect the rest of the philosophy to be coherent?