In Chapter 16 of The Doctrine of the Mean, Ti Wu (體物) is used for describing the power of spiritual beings, and Chu Hsi interpreted it as "form the substance of all things". In Chu Hsi's view, Ghosts and Spirits were positive and negative spiritual forces in nature, the contraction and expansion of them were basically functioning as principles of everything, and nothing could be existent without them. As a result, Ghosts and Spirits were no longer merely mystical things which lay people usually held, and they couldn't be considered as beings after people died. On the other hand, the contraction and expansion were real function of Qi (氣), which formed the substance of all things, and guaranteed the great ultimate (Heaven, 天) implementing in everything of the nature. Both these aspects were established to resist the doctrines of Buddhism.