dichotomy
noun [ C usually singular ] formal uk/daɪˈkɒt.ə.mi/ us/daɪˈkɑː.t̬ə.mi/
一分为二，对立
a difference between two completely opposite ideas or things
There is often a dichotomy between what politicians say and what they do. 政治家的言行之间常有天壤之别。
Compare: duality