sentences:  According to the theory, primary qualities are measurable aspects of physical reality; secondary qualities are subjective.Gottfried Leibniz was an early critic of the distinction, writing in his 1686 "Discourse on Metaphysics" that "[i]t is even possible to demonstrate that the ideas of size, figure and motion are not so distinctive as is imagined, and that they stand for something imaginary relative to our perceptions as do, although to a greater extent, the ideas of color, heat, and the other similar qualities in regard to which we may doubt whether they are actually to be found in the nature of the things outside of us.