SilasBarta:

You can quite clearly recognize that there is a being of approximately the same composition and configuration in the same location from one moment to the next.

That's why I wrote that "the concept [of personal identity] is more or less coherent assuming the traditional biological constraints on human life." It falls apart when we start considering various transhuman scenarios where our basic intuitions no longer hold, and various intuition pump arguments provide conflicting results.

Arguably, some of the standard arguments that come into play when we discuss these issues also have the effect that once they've been considered seriously, our basic intuitions about our normal biological existence also start to seem arbitrary, even though they're clearly defined and a matter of universal consensus within the range of our normal everyday experiences.