Reichenbach's Criticism of Plato's "Forms" Argument
Prof. Brian Clayton
 

Condensed from Bruce R. Reichenbach, Is Man the Phoenix? A Study of Immortality (Grand Rapids, MI: Wm. B. Eerdmans Publishing Co./Christian University Press), 1978.
 

1. Reichenbach formalizes Plato's argument as follows (p. 116):

1. Forms cannot be their opposites.

2. Properties which are named after these forms cannot admit of their opposites without withdrawing or ceasing to exist.

3. A thing which has a certain property essentially cannot admit of the opposite of that property, without withdrawing or ceasing to exist.

4. The essential property of the soul is life.

5. The opposite of life is death.
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6. So, the soul cannot admit of death without withdrawing or ceasing to exist.

7. Whatever cannot admit of death is immortal.
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      8.  So, the soul is immortal.
9. Whatever is immortal is imperishable.

10. Whatever is imperishable cannot cease to exist.
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11. So, the soul cannot cease to exist, but withdraws from that which admits of death, the body.

 2. Reichenbach does not take exception to this argument down through step 8. By the time reaches step 8, one knows that the soul is immortal because (by definition in step 7) it cannot admit of death. At this point, then, there are two possibilities for the immortal soul: either it withdraws (and survives) or it ceases to exist. Socrates, of course, needs to show that the soul survives (i.e., withdraws) rather than ceases to exist. So, Socrates needs to show that whatever is immortal cannot cease to exist. If he can show this, then he can show that the soul (which is immortal) will withdraw (flee) rather than ceasing to exist. So, the key moves in the argument will occur in steps 9 and 10.

3. It is in premises 9 and 10 that Reichenbach identifies a problem with this argument: the argument either equivocates or begs the question. Equivocation occurs whenever the same word has more than one meaning in an argument. Begging the question occurs whenever one simply assumes the truth of that which one is supposed to be proving. The word that causes all the problems (according to Reichenbach) is the word "imperishable," in premises 9 and 10.

4. Let's begin with the following definition of "imperishable"

                           (D1) Something is imperishable if and only if it is not subject to organic disintegration.

If we understand "imperishable" along the lines of (D1), then premises 9 and 10 would read as follows:

9. Whatever is immortal is not subject to organic disintegration.

10. Whatever is not subject to organic disintegration cannot cease to exist.

 On this reading of "imperishable," premise 9 is probably true but premise 10 seems to be false. That is, it is possible that something that is not subject to organic disintegration could still cease to exist. For example, the Sun is not subject to organic disintegration. It cannot rot and decay. Yet it is still possible that the Sun cease to exist. The Sun could simply be annihilated (be destroyed). After all, rot and decay are only one way in which something can be destroyed. So, ruling out rot and decay is not enough to tell us that there is no other way in which a thing could be destroyed. The only way in which premises 9 and 10 could both be true is that a different meaning is used for "imperishable" in premise 9 than is used for "imperishable" in premise 10. But this, of course, is the fallacy of equivocation.

5. This suggests an alternative definition of "imperishable."

                           (D2) Something is imperishable if and only if it cannot be annihilated.

On this understanding of "imperishable," premises 9 and 10 read as follows.

9. Whatever is immortal cannot be annihilated.

10. Whatever cannot be annihilated cannot cease to exist.

 On this reading, premise 10 seems clearly to be true. The problem, now, is that premise 9 begs the question. That is, Socrates needed to show that, that which does not die is that which cannot be annihilated. Premise 9 simply asserts this claim without argument.

6. So, Reichenbach concludes that Socrates has not shown what he needed to show; Socrates has either equivocated or begged the question.

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Copyright 1998 by David H. Calhoun and Brian B. Clayton.  This page last updated on May 28, 1998.