This is very useful for explaining the Epicurean position (in opposition to the Skeptics) that concepts such as "fair" and "foul" and "larger" and "smaller" are no less real than gold or silver, even though (the Skeptics argue) that the former are unreal because they are perceived and interpreted differently by everyone, while the latter are real because they are perceived the same everywhere.
Or do you think, on the basis of the foregoing argument, that someone would not suffer the troubles which I mention but rather would make it convincing that fair, foul and all other matters of belief are falsely believed in, just because unlike gold and similar things they are not the same everywhere? After all, it must stare everybody in the face that bigger and smaller are also not perceived the same everywhere and in relation to all magnitudes […] So too with heavier and lighter. And the same applies also to other powers, without exception. For neither are the same things healthy for everybody, nor nourishing or fatal, nor the opposites of these, but the very same things are healthy and nourishing for some yet have the opposite effect on others. Therefore either they must say that these too are false –things whose effects are plain for everyone to see –or else they must refuse to brazen it out and to battle against what is evident, and not abolish fair and foul as falsely believed in either, just because unlike stone and gold they are not the same for everybody […] Relative predicates do not have the same status as things said not relatively but in accordance with something’s own nature. Nor does the one kind truly exist but the other not. So to expect them to have the same attributes, or the one kind to exist but the other not, is naive. And there is no difference between starting from these and eliminating those and starting from those and eliminating these: it would be similarly naive to think that since the bigger and heavier and whiter and sweeter are bigger than one thing but smaller than another, and heavier, and likewise with the other attributes, and since nothing has the same one of these attributes per se as it has in relation to something else, in the same way stone, gold and the like ought also, if they truly existed, likewise to be gold in relation to one person while having the opposite nature in relation to another; and to say that, since that is not the case, these things are falsely believed in and do not really exist (On irrational contempt,XXIII, 26-XXVI, 23). (Quoted from Sedley - Epicurean Theories of Knowledge from Hermarchus to Lucretius And Philodemus)
Sedley comments about this:
The opponents can be seen to draw heavily on Platonic dialectical materials in order to launch their attack on the reality of values, in particular in their contrast between the universally agreed determinate nature exhibited by minerals and the cultural relativity of values. As one might expect of the New Academy, this sceptical argument borrows its materials freely from the text of Plato (Phaedrus, 263a, cf. also Euthyphro, 7b-d, Theaetetus, 172b). More remarkable is how Polystratus, in his reply,appears himself to draw inspiration from Plato –a strategy with all the more ad hominem force when directed against Plato’s own self-declared successors. Plato had indeed never intended by this contrast between minerals and values to impugn the reality of the latter, any more than he had meant to infer from the relativity of large(r) and small(er) to their unreality. On the contrary, at Sophist 255c he had presented an exhaustive division of beings(ὄντα) into absolute and relative, a bicategorial scheme which became formal Academic doctrine under his second successor Xenocrates (F15 Isnardi Parente2).
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... He resourcefully points out that the mere existence of an ontological difference between the two categories does not entail that one or other of them will fall short of reality. Anyone who thinks otherwise, he ingeniously adds, could as easily arguethat, since such relative predicates as beneficial and harmful manifestly arepart of the structure of reality, it must be the non-relative items such as minerals that are unreal!
