Heraclitus was obviously no exception, indeed he probably expressed the universality of change more clearly than his predecessors; but for him it was the obverse idea of the measure inhering in change, the stability that presists through it, that was of vital importance.(The Presocratic Philosophers, by G.Kirk)
"Obverse idea" refers to the "measure","logos", which is the unchangeable in the changable things. So it seems that "obverse" is presumed by the author to mean "reverse": unchangable vs change.
But with second thought, I think it is not so. The two theory both are valid for Heraclitus, therefore they are not opposing, but complementing each other.
I think this sort of contrastive relation is perfectly expressed by "obverse", I cannot find another word to replace it. But by using Google N-gram viewer, I find that "obverse" is extremely rarely used. So does anyone have other suggested alternatives?