Mencius may have been reacting to Mohism. Mozi (470–391 BC) had earlier initiated a shift in focus to more natural and objective, less culturally relative way of grounding normative judgment.  His claim that 天 tiānnature:sky exhibited a tendency to a course leading to human utility or well-being.  So humans should use that natural norm, the 辯 biàndistinction between 利害 lì-hài benefit-harm in constructing our social dào, including the norms of language.