(a) IRV and ERV: Inspiratory Reserve Volume (extra air inhaled beyond normal, ~2500 mL) vs Expiratory Reserve Volume (extra air exhaled beyond normal, ~1000 mL).
(b) Inspiratory capacity and Expiratory capacity: Inspiratory capacity = Tidal Volume + IRV; Expiratory capacity = Tidal Volume + ERV.
(c) Vital capacity and Total lung capacity:  Vital capacity = TV + IRV + ERV; Total lung capacity = VC + Residual Volume.