07 Mar 2009
Ghosts of Memory

In the small hours of the morning, as I wander randomly over the ‘Net, something reminds me of Ghost in the Shell. One of the pervasive issues in GITS is what it means to be human in a society where entire bodies can be replaced with prosthetics, consciousness transferred from one construct to another, and strong AI is becoming indistinguishable from “human”.

That in turn reminds me of a long-ago (80’s ?) discussion with a friend about whether gradual replacement of all “components” over time would leave someone the “same” person, and would that be qualitatively different that a sudden replacement of everything at once. In essence, I suppose, it came down to whether there was continuity of sense-of-self.

The truth is that it’s happening to us daily, without need of any silicon substrate for our consciousness; or plastic, metal, and ceramic parts to replace lopped off limbs or damaged organs. According to “Body Story”, a Discovery documentary I happen to be watching (one more disc to go), almost no part of anyone’s body is over 10 years old; some parts are renewed after only a few days.

In any case, like many philosophical quandries this actually has a name and a long history. Wikipedia says, “The Ship of Theseus paradox, also known as Theseus’s paradox, is a paradox that raises the question of whether an object which has had all its component parts replaced remains fundamentally the same object.” Quoting from Plutarch’s “Theseus”:

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 among 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.

Elsewhere he quotes Heraclitus:

“It is impossible to go into the same river twice”, said Heraclitus; no more can you grasp mortal being twice, so as to hold it. So sharp and so swift its change; it scatters and brings together again, nay not again, no nor afterwards; even while it is being formed it fails, it approaches, and it its gone.

The whole XVIII paragraph eerily parallels the “Body Story” segment on aging.

The Wikipedia article also mentions more recent variations of the paradox — such as George Washingon’s axe, John Lock’s socks, Jeannot’s knife, and contemporary references to it in fiction and media. I could not help but form the mental image the ship of Theseus, made of wood hewn by Washington’s axe, floating on Heraclitus’s river, me aboard and wearing Lock’s socks, mended with Jeannot’s knife. (Sorry, sorry).

It occurs to me that programmers must also decide what it means to be the “same” thing. For example, in Java you must be careful in choosing == vs .equals(); in Lisp, you must pick =, EQ, EQL, EQUAL, or EQUALP.

Perhaps, as said in Ecclesiastes, “That which has been is that which shall be; and that which has been done is that which shall be done: and there is no new thing under the sun.”

Category: philosophy
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