The in-place replacement proponents claim that you don't survive by copying, but do survive by in-place replacement of parts. In what follows, Parfit presents the most significant challenge to the survival- through-brain-repair alone method to date.

Parfit REASONS AND PERSONS p.474-475:

"In Case One, the surgeon performs a hundred operations. In each of these, he removes a hundredth part of my brain, and inserts a replica of this part. In Case Two, the surgeon follows a different procedure. He first removes all of the parts of my brain, and then inserts all of their replicas....In both of my cases, there will later be a person whose brain will be exactly like my present brain, ....Can this be the difference between life and death? Can my fate depend on this difference in the ordering of removals and insertions? Can it be so important, for my survival, whether the new parts are, for a time, joined to the old parts?"