程頤立足於孟子「踐形」說之「形」，對傳統生化理論和道家「形變」說做了創造性改造，提出「形－性」統一的「氣化－形化」生化理論。這既是與宋儒道二教爭奪孝道解釋權的嘗試，也在理學傳承中起到了重要作用，為理學生化論提供了基本模型。

On the basis of Mencius “jian xing” (踐形) theory, Cheng Yi reformed the traditional theory about how all things are produced. He put forward the thought of “xing hua” (形化) in the case of unification of “form” and “essence”. This thought is a response of the traditional theory about how all things are produced and the circumstance that Buddhist and Taoist separated “form” and “essence” in the Northern Song Dynasty, also establishing absoluteness and legitimacy of the filial duty. Therefore the “xing hua” thought of Cheng Yi is inherited and developed by scholars, playing an important role in Neo-Confucianism, also is the bridge between the four masters in the Northern Song Dynasty.