Information about the physical world is excluded from visual stimuli by the nature of biological vision (the inverse optics problem). Nonetheless, humans and other visual animals routinely succeed in their environments. The talk will explain how the assignment of perceptual values to visual stimuli according to the frequency of occurrence of stimulus patterns resolves the inverse problem and determines the basic visual qualities we see. This interpretation of vision implies that the best (and perhaps the only) way to understand visual system circuitry is to evolve it, an idea supported by recent work.