"Human cells are continuously replaced, and much of the body is rebuilt over time. By the age of 65, you will have gone through six skeletons, four sets of muscles and guts, and your red blood cells will have been renewed almost 200 times. So can you be regarded as the same person you were 20 years ago?" —Mark Stephens, The Philosophy Notebook The concept of self-identity is problematic indeed. What do we mean when we refer to ourselves as "I"? Understanding the Problem Imagine that you're at your friends house, chilling on the couch while they're fixing bacon cheddar burgers (your favorite) in the kitchen. All of a sudden you hear your friend yelp in pain: "Shit!" "What happened? Are you okay?" "Yeah, I just nicked my hand." I nicked my hand? Usually, claims to possession are to external objects, so who is this I that the hand belongs to? You could ask your friend: are you not your own body? If your frien...