Cambridge Changes of Color

Abstract

Locke's porphyry argument at 2.8.19 of the Essay has not been properly appreciated. On my reconstruction, Locke argues from the premise that porphyry undergoes a mere Cambridge change of color in different lighting conditions to the conclusion that porphyry's colors do not belong to it as it is in itself. I argue that his argument is not quite sound, but it would be if Locke chose a different stone, alexandrite. Examining his argument teaches us something about the relation between explanatory qualities and real alterations and something about the ways that colors inhere in bodies.