Polarity — "everything is dual"

The fourth principle: opposites are the same thing differing in degree — heat and cold on one thermometer — and so one pole can be transmuted into the other. The Tree says this structurally with its two outer pillars: Chesed and Gevurah, expansion and restraint, mercy and severity, not two forces but one measure read at two ends, held in balance by the middle pillar. The Kabbalist adds what the principle omits — that the balancing is moral work, not merely mental adjustment.