Every one of us has a particular philosophical worldview: a way in which we perceive ultimate reality. Often there are competing philosophical outlooks within a given culture, particularly in one as pluralistic as our own. One way to readily identify someone’s philosophical presuppositions is to ask them their take on some specific issue/problem. I’m going to do that with you to determine your philosophical viewpoint on the issue of personal identity. What gives us our identity? Does our identity remain the same over time?
Let’s say person X suffers a coma at age 35. He is in a coma for 7 years. During that time nearly every cell in his physical body has been replaced. At age 42 he wakes up from his coma but cannot remember anything about his past.
Question: Is he still person X, or has he become a different person: person Y? Why or why not?
Consider another problem. In ancient Greece there was an Athenian king by the name of Theseus. He was both a warrior and a sailor. Plutarch makes reference to his ship:
The ship wherein Theseus and the youth of Athens returned had thirty oars, and was preserved by the Athenians down even to the time of Demetrius Phalereus, for they took away the old planks as they decayed, putting in new and stronger timber in their place, insomuch that this ship became a standing example of the philosophers, for the logical question of things that grow; one side holding that the ship remained the same, and the other contending that it was not the same.
(Plutarch, “The Life of Theseus,” in The Lives of the Noble Grecians and Romans, trans. John Dryden, rev. Arthur H. Clough (New York: Random House, n.d.), 14.)
Question: Was the ship repaired or replaced? Was the ship that existed in Phalereus’ day the same ship that Theseus sailed on? Why or why not?
Thinking to Believe 
June 25, 2006 at 8:25 am
It appears this post was too esoteric to perk your interests, so let me finish it off.
What makes you you? How do you remain yourself over time? Think of it, if you are 28 years old you have had approximately four different bodies! How can you say the person who learned to ride a bike at five is the same person who is reading this blog today? This is the problem of identity, and it is very important. It affects a host of issues including abortion and the theism vs. atheism debate.
There are two basic types of identity: substances, property-things.
Property-things are systems of parts standing in external relations with one another (an external relation is one that is not necessary for the continued existence of the parts were they disconnected from the whole), each of which is capable of existing on its own independent of the other parts. The parts of a property-thing can change over time, with some parts being added and some being removed. But as the parts change, so does the thing itself. Identity for a property-thing is not absolute, but degreed. Identity for a property-thing can even be lost entirely.
An example of a property-thing is a table. If you remove a leg from a table both the leg and the rest of the table continue to exist, but the table qua table ceases being the thing it once was. Its identity has changed. Why? Because property-things cannot lose and gain parts while maintaining absolute identity over time. As the parts change, so does the identity. It becomes something new. If you continue to remove legs and leaves from the table, eventually the table will cease to exist altogether as such.
Theseus’ ship is another example of a property-thing (what follows is the answer to question two). The ship Theseus sailed on ceased being the same ship once the very first plank was replaced; i.e. its absolute identity was lost. Its identity continued to be slowly lost as each plank was replaced until eventually all semblance of its original identity was eradicated.
Why this is so becomes clear if we change the original story a bit (compliments of William Craig). Let’s say each time a plank or nail of Theseus’ ship was replaced, it was replaced with green jello rather than wood. After every plank and nail had been replaced with green jello would it be the same ship?
Let’s take it one step further. Let’s say each plank and nail was stored in a warehouse after being removed. After every plank and nail had been replaced shipbuilders rebuilt the ship from ground up using those pieces. Now there is a ship consisting wholly of green jello, and a ship consisting wholly of wood. Which ship is Theseus’ ship? Clearly it is the ship made of the wood that constituted the original ship.
A substance, on the other hand, is an irreducible unity of parts; an abiding, unifying center of being that continues to exist transtemporally. Substances consist of inseparable parts standing in internal relations with one another (an internal relation is one that inheres within the parts themselves, and is necessary for the continued existence and identity of the parts), each of which is incapable of existing on its own and/or maintaining its identity independent of the other parts. The substance maintains absolute personal identity even as its parts change. Identity for a substance is absolute, non-degreed, and cannot be lost.
A human person is an example of a substance. Personhood is rooted in a substantial, rational soul. That is what allows us to remain the same person through the process of physical change. Change presupposes sameness. If we say Jimmy changed from being 3’ tall to being 6’ tall, then Jimmy must be present throughout each step in the process of the change. The person we were when we were 7 years old is the same person we are today even though most of our body’s parts have changed several times during that period of time. Our personal identity is not rooted in the physical parts of our body, and thus it does not change over time. In fact, our substantial self is what undergirds and directs all of our body’s changes.
To answer the first question, then, person X who laid comatose for seven years, only to awake from his coma with complete amnesia is still person X. His personal identity is not attached to his changing body, nor to his mental states. Person X is a substantial soul whose essence remains the same through physical and mental change. We are not our bodies, and we are not our brains. We are substantial souls of a rational sort, who endure through physical change, and even beyond the physical body itself.
Atheists have a hard time grounding absolute personal identity because they deny the soul, and pro-abortion advocates treat the unborn as a property-thing whose properties are not valuable because they have not yet matured to look like the properties of post-natal human beings. In both cases we end up with a flawed view of man because of a flawed philosophical anthropology relating to identity.
If pro-abortion advocates understood humans as substances rather than property-things they would see that the identity of a three week-old embryo is the same as a 30 year old female. Human identity does not change over time. We are what we are when we come into being, and we remain that until the day we die. Our external physical properties change, but our substance (in which resides value) remains the same.
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