This chapter finds two versions of the distinction between primary and secondary qualities in Galileo, Descartes, Boyle, and Locke. Although agreeing that primary qualities are physically basic properties of extended particles (including size, shape, position, and motion), these authors differed on whether secondary qualities such as color exist only in the mind as sensations or belong to bodies as powers to cause sensations. Kant was initially a metaphysical realist about primary qualities as spatialized forces (vs. bare extended particles), before placing (...) space among the appearances in his critical period. Space becomes the subjective form in which transcendently real forces and relations appear. Kant viewed color as a subjective sensation in the mind, whereas Helmholtz treated color as a power to cause sensations. Helmholtz was initially a realist about primary qualities as spatialized masses and forces, but he later adopted the epistemically modest view of space as the subjective form in which forces and relations appear. (shrink)

Gary Hatfield examines theories of spatial perception from the seventeenth to the nineteenth century and provides a detailed analysis of the works of Kant and Helmholtz, who adopted opposing stances on whether central questions about spatial perception were fully amenable to natural-scientific treatment. At stake were the proper understanding of the relationships among sensation, perception, and experience, and the proper methodological framework for investigating the mental activities of judgment, understanding, and reason issues which remain at the core of philosophical psychology (...) and cognitive science. (shrink)