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 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. Hatfield presents these important issues as living philosophies of science that shape and are shaped by actual research programs, creating a complex and fascinating picture of the entire nineteenth-century battle between nativism and empiricism. His examination of Helmholtz's work in physiological optics and epistemology is a tour de force. Gary Hatfield is Associate Professor of Philosophy at the University of Pennsylvania.