Abstract

Locke establishes the primary-secondary quality distinction in two steps. First, he identifies the primary qualities by means of a separability argument that involves transdictive inference about the properties of the minute, imperceptible parts of matter. Second, he identifies the secondary qualities by means of a dispensability argument that relies on the principle that bodies normally act by ‘impulse.’ I suggest this principle is also justified through transdictive inference. This allows us to see Locke’s claims about primary and secondary qualities as unified, fallibilist and rooted in empiricism and the methodology of Newtonian science.