Mind was the oneness of form and function. The change from an old theory to a new one about zhong 中 (the mean) and he 和 (harmony) was a shift from the idea of the separate form of nature and function of mind to one about both form and function of mind. Form was both the form of the spirit of the mind and of the substantiality of nature (not the same as substantial realities in substantialism); it was the integration of vacancy and substantiality, the integration of mind and nature. In contrast, function meant both feelings and perceiving action. It was infeasible to interpret function without reference to form; likewise, it was impractical to talk about perception without mentioning nature. On the other hand, a knower represented nature through concrete things and his actions, and a perceiver enlightened himself, realizing the self-consciousness of nature as a whole. Mind, nature, and perception could be interpreted as a whole, and these three could be separated too. Viewed in general, mind, nature, and principles were oneness; observed separately, nature differed with principles: nature meant principles, but perception was the quintessence of qi. The unfolding of perception, however, had its independence, and could be easily influenced by qi; thus, it was necessary to transform and cultivate qi-related temperament. Realistically, a man needs to face up to himself and to transform himself, and this sentiment is inspiring for today.