Knowing about knowledge allows one to predict and understand one’s actions and the actions of others—in short, the behavior of the world, such that internal states of numerous kinds correspond heuristically to the world’s behavior. Knowledge is our main tool for linking the world of imagination to the world of objects, which we refer to as the external world. Hence, it is not surprising that gaining access to parts of the knowledge of others and ourselves is one of the key necessities in reasoning, learning, teaching, and judging whether someone can be considered fit to operate within critical processes in the world. Thus, from expertise to the very simplest learning or reasoning processes, it is absolutely crucial to know about what someone might know—it is ...