[MD] Protagoras and "Measure"

[MarshaV]

   "The clearest form of the argument is given by Aristotle.  In the fourth book of the *Metaphysics," 
Aristotle advances two decisive principles regarding primary substance (*ousia*): (i) necessarily, 
for every attribute, a substance either possesses that attribute or it does not, which is Aristotle's 
version of the principle of excluded middle; and (ii) for any substance, if anything may be 
predicted of it then, necessarily, its attributes cannot be accidents only, or only apparent 
properties, the violation of which Aristotle takes to entail contradiction.  Protagoras, apparently, 
violates both -- which shows at the least that relativism was thought in the ancient world to 
involve a restriction on, or abandonment of, the principle of excluded middle.
   Now,*if* it is not true that reality is changeless, then, of course, (ii) must be given up; and 
if (ii) is abandoned, then, on Aristotle's own reading of (ii), (i) must be given up also.  But the 
ancients understood the doctrine, "man is the measure," to entail at least that reality is not 
changeless -- also, therefore, that if man can rightly claim to have knowledge, than, on Protagoras' 
argument, knowledge cannot be addressed to what is changeless in reality.  This much at least 
yields a stalemate between Aristotle and Protagoras: thus far, neither one's thesis is obviously 
incoherent.  But even this much favors Protagoras, because Aristotle holds that the violation 
of (i) and (ii) yields contradiction.  More would need to be said.
   Aristotle does have more to say.  There is another argument, a bridge argument, that is decisive 
for Aristotle:  "if not all things are relative, but some are self-existent, not everything that appears 
will be true"; and *that*, which is tantamount to (ii), must, *somewhere* in Protagoras' argument, 
yield the denial of those properties of particular substances *that are changeless.*  Nothing could 
be more reasonable.  The only trouble is that Protagoras rejects the thesis that there *is* something 
changeless, and Aristotle nowhere shows convincingly that *that* produces contradiction, except, 
trivially, *by* presupposing the truth of what must first be shown to be true.  So Aristotle fails.  
Certainly, in our own time, nearly every prominent thinker either believes that reality is not 
changeless or believes that it is not demonstrably true that believing *that* cannot but be 
incoherent."
    (Margolis, Joseph, 'The Truth About Relativism' (Paperback), pp.77-78)






  
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