 Green thinks that this empiricist program suffers rot at the foundations; he thinks that simple sensory experience that is not relational and in which the mind plays a purely passive role is impossible. All experience presupposes certain formal conceptions that the subject of experience employs—those of subject and object, substance and quality, cause and effect, spatiality, and temporality (Works I 12–13, 16–17, 40–41, 43–50).