Some thought experiments before getting into definitions and discussions of identity (as discussed by me and some college friends during a recent visit; I can’t find the website with them in quiz form):

EDIT: Todd found it! The questions below, in quiz form.

  1. You are traveling to Mars.  You have two options for getting there: spacecraft or teletransportation.  The spacecraft is pretty dangerous: there’s a 50% chance you’ll die in transit.  The teletransportation method will disassemble you at the origin (Earth), transmit you as information, and reconstruct you at the destination (Mars).  Which do you choose?
  2. You are suffering from a peculiar neurological malady.  You have two options: you can let it run its course, or you can go through a process designed to fix it.  If it runs its course, your brain will be screwed up and you’ll have a radical personality shift.  The process to fix it involves replacing all of your brain, piece by piece, with new techy brainlike material – you’ll retain your current personality (totally cured) but when the process is complete, none of your original brain will remain.  Which do you choose?
  3. Scientists discover the nature of the soul (or agency, or consciousness, whatever you prefer), around the same time that you contract a deadly disease.  It turns out the soul will leave a dead body and attach to a newborn, a sort of reincarnation.  You have two options: you can let the deadly disease run its course, have about a 50/50 chance of dying, and your soul will reincarnate to a new host, or you can be put into cryostasis long enough to cure the disease.  The same research which determined the nature of the soul also found that this cryostasis operation will destroy your soul.  Which do you choose?

Another really interesting essay on identity, via Kelly: Where Am I?