In most discussions of memory, philosophers have made reference to only episodic memory -- that is, memory of particular episodes and events in one's life. The basic idea was that if you have a memory of doing something, then you are the same person as the one who did the act. Objections to this theory frequently pose problems where the subject's memory is impaired -- is he then a different person? To get around these dilemmas, Grice elaborated the theory to allow a variety of memory-linkages, which can combine to form a single person. The need for such a complex theory can be avoided by recognizing that episodic memory is only a small part of the memory humans use. There are also a wide variety of implicit memories, i.e., memories of which we have no conscious awareness, but which nonetheless affect our behavior. Examples include motor skills (e.g., driving a car), perceptual skills (reading in a mirror), priming effects, and many more. In addition, we all have a set of personality traits, habits, and quirks which make every person different from everyone else. These can change over time as a result of experience, injury, or chemical influences, just as memories do. When all these factors arer considered, most of the dilemmas posed by philosophers are not dilemmas at all.
The second pillar of the theory comes from the relatively new field of fuzzy logic. In traditional Boolean logic, statements are either True or False; there are no half-truths. I believe that this mathematical system strongly influenced philosophy for the last several centuries. Recently, however, the field of "fuzzy logic" has been developed as a superset of Boolean logic. Truth values in this system may take any value in the range from True to False, and are typically described with terms such as "mostly true", "partly true", "mostly false", and so on. The application to identity is straightforward: we say that person A and person B are the "same person" to the extent that A and B share common experience (as described above). Today, no two people at the same time have any common experiences at all (they always differ by at least the point of view), and so everyone is a unique person. On the other hand, I share nearly all my experiences with the person who began this essay; that person, therefore, was me. When I go to bed, I can reasonably expect the person who wakes up in my bed to be me, as well. Thus the theory handles today's commonplace situations just as well as Boolean memory theory; in the Cases, we will see some situations where the fuzziness applies.
Fuzzy experience theory provides a view of identity which is simple and logically consistent; its implications fit well with our "common-sense" views of persons. As the Cases will show, it also handles unusual cases in a way that is just as parsimonious and intuitive. And these are the two tests of a philosophical system: Is it consistent with itself and with known facts? And, Do the implications make sense? For fuzzy experience theory, the answer to both is Yes.