The foregoing chapters have highlighted the extent to which Dewey was inspired by scientists and philosophers who set forth a vision of the world as a place undergoing constant development instead of a place created once and for all by natural laws or by an almighty God. Hegel, Darwin, and pragmatists such as James and Pierce were process thinkers, who preferred to take their points of departure in the concepts of development and becoming rather than in more static conceptualizations of existence. When one inquires into the fundamental structure of the world, including what truly exists (for instance, the changeable versus the unchangeable), one enters the philosophical discipline known as metaphysics. The present chapter concerns Dewey’s metaphysical ideas. These are regarded as philosophically fundamental for his thinking on psychology, ethics, and pedagogy, which shall be presented in later chapters.