bivalence noun. 
[esp. Chemistry bʌɪ'veɪl(ǝ)ns, esp. Cytology 'bɪv(ǝ)l(ǝ)ns] L19.[from BI- + VALENCE noun1.]1.  Chemistry & 
Cytology. The quality of being divalent. 
L19.2.  Logic. The existence of only two truth values; 
spec. in 
principle of bivalence: that every proposition is either true or false. 
M20. ■   bivalency noun L19.  [TahlilGaran] English Dictionary ▲