'I really don't think Shakespeare added much if anything to humanity's stock of "truths."'
--He added Hamlet.
--He added Henry IV, part 1. (historical drama)
--He recast the tragic mode from the classical heroic ability-to-meet-fate, to the more modern form of tragedy as existential paradox.
I don't know if these are "truths," but they are representations of experiences/realities that did not exist in the classical age.
Joanna