Post Author: Bill Pratt

The next major difference between mental and physical entities is how personal identity through change is handled.  Dr. Moreland asks us to…

Imagine a wooden table that had all its parts removed one by one and replaced with metal parts. Now suppose someone took the original wooden parts and made a new table.  Which one would be the original table – the metal one or the wooden one?  The answer seems to be clear.

The original table would be the wooden one. Why? Because if something is made out of stuff called parts, then it cannot remain identical to itself if it gains new parts and loses old ones. If a table here and now is going to be the very same table as one that was here, say an hour ago, this table must be made out of the same stuff as the one an hour ago. If not, then they are different tables. In general, physical objects cannot remain literally the same if they gain new parts and lose old ones.

But what about people?  How do we view the identity of human persons who are constantly losing parts?

Each moment I lose hundreds of thousands of skin cells, some hair, and other microscopic parts. In fact, every seven years my cells are almost entirely replaced. Do I maintain literal, absolute sameness through change?

Dualists argue that persons do maintain absolute identity through change, because they have, in addition to their bodies and current mental experiences or mental capacities (say, the capacity to remember a childhood event), a soul that remains constant through change. Personal identity is constituted by sameness of soul, not sameness of body or mental abilities, such as memory.

How do physicalists handle personal identity through change?

Physicalists . . . have no alternative but to hold that personal identity through change is not absolute. Usually they argue that persons are really ancestral chains of successive, momentary “selves” (called person-stages) that are connected with one another in some way. At each moment a new self exists (since the organism is constantly in flux, gaining new parts and mental experiences and losing old parts and mental experiences), and this self resembles the self prior to and after it.

The relation of resemblance between selves, plus the fact that later selves have the same memories as earlier selves and the body of each self traces a continuous path through space when the whole chain of selves is put together, constitutes a relative sense of identity. At this moment I merely resemble a self that existed a moment ago: My body resembles that body; my memories resemble the memories of that earlier self; my body was reached by the body of the earlier self through a continuous spatial path.

So substance dualists hold to a literal, absolute sense of personal identity, and physicalists . . . hold to a loose, relative sense of personal identity that amounts to a stream of successive selves held together by resemblance between each self in the stream— similarity of memory or brain, similarity of character traits, and/or spatial continuity. But this perspective creates certain problems for physicalism.

Next post we will look at the problems it creates.