  The parity principle says “[i]f, as we confront some task, a part of the world functions as a process which, were it done in the head, we would have no hesitation in recognizing as part of the cognitive process, then that part of the world is…part of the cognitive process” (Clark 2008, 222). As illustration, Clark and Chalmers (1998) compare the occurrent beliefs of Otto, who is afflicted with Alzheimer’s disease, to those of Inga, who has a normal biological brain. Otto keeps a notebook containing information of the sort that would be stored in the hippocampus of a normally functioning brain. When Inga wants to visit MoMA, she pulls from her biological memory the information that MoMA is on 53rd St. which prompts her to take a subway to the destination. When Otto has the same desire, he consults his notebook in which is written “MoMA is on 53rd St.”, which in turn induces his trip to that location. By stipulation, the representation of MoMA’s location in Otto’s notebook plays an identical functional role to the representation in Inga’s brain. Hence, by the parity principle, the notebook entry is a memory—an occurrent belief about the location of MoMA. The notebook is thus home to constituents of many of Otto’s cognitive processes.