Here. The host, Robert Kuhn, "an old brain scientist" as he describes himself, can't seem to wrap his mind around the argument. The argument goes like this, where 'B' denotes (rigidly designates) a person's body or else that part of a person's body (presumably the brain or a part of the brain) with which the materialist wishes to identify the person.
1. If x = y, then whatever is true of x is true of y and vice versa. (Leibniz's Law)
2. 'Possibly exists when B doesn't' is true of me but not true of B.
3. Therefore: I am not identical to B. (From 1, 2 by Universal Instantiation and Modus Tollens)
Kuhn, at or around 4:26, objects that the distinction between a person and his body is "a possibility, an indeterminate fact." No! The possibility of my existing when B doesn't entails the actual difference between me and my body, not the mere possibility of such a difference. And Kuhn still doesn't get it after Plantinga explains it.
The argument is valid in point of logical form, and (1) is a principle than which a more luminous one cannot be conceived; but what is the evidence for (2)? How does one know that it is possible that one exist when one's body or brain doesn't? Because one can imagine that state of affairs. Plantinga reminds us of Franz Kafka's short story, "The Metamorphosis" in which the protagonist, Gregor Samsa, wakes up one morning with the body of a beetle. It is imaginable that one retain one's conscious identity while possessing a beetle body, and further imaginable that one's human body be destroyed; this, Plantinga maintains, is evidence for the truth of (2).
It didn't occur to Kuhn to question whether imaginability is evidence of possibility.
Recent Comments