Duality

- The central Igbo notion (Achebe endorsed and extended by Umeh): nothing stands alone; every existence has its counterpart; the human world doubles in the spirit world; the person is completed by the Chi.

- Institutional dualities: Dibia/Ofeke; Ndi Ma Mmuo/Ogbodu (initiated/uninitiated into masquerade); Ifite/Ezi territorial halves; alternating Odo year/Ofeke year; okwu/ukpolo four-day phase cycles (holy/dangerous); ijo na mma — evil and good arriving together (initiation rituals shunt the baleful half to the ground).