Thinking is a private activity. Thought can't be accessed by anyone else. This concept of thoughts is described as Cartesian after René Descartes. ‘The inner sanctum’ focuses on the epistemological elements of the Cartesian notion of thought by considering two themes: first-person thought is transparent (one's own thoughts are immediately accessible to one), and third-person thought is opaque (the thoughts of other people are not immediately accessible to one). These notions have been heavily criticized over the last century. Who are the most influential critics of these ideas? Can we completely conceal our thoughts? It has been argued that human thought has its roots in the publicly accessible space of perception and action.