Full Idea
Protagoras was the first to claim that there are two contradictory arguments about everything.
Gist of Idea
Protagoras was the first to claim that there are two contradictory arguments about everything
Source
report of Protagoras (fragments/reports [c.441 BCE], A01) by Diogenes Laertius - Lives of Eminent Philosophers 09.51
Book Reference
'The First Philosophers', ed/tr. Waterfield,Robin [OUP 2000], p.211