I am currently writing an essay on Protagorean Relativism. I am to provide my opinion on the subject.
Take for example, one ill and one healthy man. They both drink the same orange juice, however it is
sweet to the healthy man and sour to the sick man. In Protagorean Relativity is the orange juice
unchanging or always changing according to who perceives it?
As far as Protagoreanrelativism goes, there's a nice little exposition of it at:
http://www.arts.ubc.ca/philos/russellj/100lec00.htm. And I'm sure there are many others. As I
understand it, it depends on what you mean by the "orange juice", whether that refers to the "actual"
juice lying "behind" (so to speak) one's sensory impressions, or the juice considered strictly as one
sees, tastes, etc., it. The latter, as the source of "truth", if I understand that position correctly, is the
Protagorean thesis. In that vein, you might also look at various writings by Bernard Williams, who is
very concerned with truth (I only cite one ref below).