yeah, yeah

The French have their si.  The contradicting yes.  (Of course it is also used for emphasis, but all emphasis is implicit contradiction.)  For lack of a si, we English speakers are forced into the use of no or any of its negative kin as a kind of whole-word prefix to an affirmation: No, I'm going.  Or else we made the affirmation bigger: Oh, yes!  Or we do without.