 Whitehead spoke of the “bifurcation of nature into two systems of reality” (1920 [1986: 30]) to denote the strategy—originating with Galileo, Descartes, Boyle and Locke—of bifurcating nature into the essential reality of primary qualities and the non-essential reality of “psychic additions” or secondary qualities, ultimately to be explained away in terms of primary qualities. Whitehead sided with Berkeley in arguing that the primary/secondary distinction is not tenable (1920 [1986: 43–44]), that all qualities are “in the same boat, to sink or swim together” (1920 [1986: 148]), and that, for example,