In both the Christian philosophy of Augustine and the Neo- Confucianism of Zhu Xi, reflections on the mind-body problem necessarily involved their understandings of individuality and relationship in human existence. Augustine regarded the human soul as a different subject from the material body, and he defined the inherent human nature as arising solely from the vertical relationship between each individual soul and God, so his thinking of individuality is characterized by the subject-object dichotomy between soul and body, ego and other, human and nature, which as a result brings about the loss of relationship. In Zhu Xi's view, the individual person is a spiritbody unity in harmony with heaven and nature, but he fails to discover the relative independence of spiritual existence and its difference from material existence, so his understanding of the relationship between body and spirit, human and heaven, diversity and oneness are finally replaced by the absoluteness and exclusiveness of "Li Yi" (the Unique Principle).