This chapter looks at the ways in which Galen posits the theoretical unity among the discrete physiological system, especially with a reference to tripartition. Unlike Platonic, the tripartition that is motivated by psychological conflict, Galen’s tripartition of physiological domains shows the three domains to be highly cooperative and co-dependent on each other. The respective material fluxes they control are together necessary for continued functioning. The chapter looks at Galen’s adoption of the popular philosophical idea that identity persists because of the form, and at his analysis of different causes, strongly influenced by the ideas of his contemporary Middle Platonists. While more popular analyses of causes explain that the body is unified in its design, it is the notion of cohesive cause, the chapter argues, that accounts for unified physiological functioning.