In his Discourse on the Natural Theology of the Chinese, Leibniz produces an interpretation of the first principle of Chinese philosophy. The present article proposes to search for the conditions of this interpretation by comparing it with the controversy between Leibniz and Descartes over the conception of substance. It will be shown that, although Leibniz applies a “hermeneutic principle” in his interpretation of Chinese philosophy, this principle is not sufficient but its usage depends on more fundamental conditions. The comparison with the Leibniz-Descartes controversy over the conception of substance allows us to identify two major conditions for the application of this hermeneutic principle, namely the dynamic theory of substance and the conception of natural theology as the foundation of physics, two subjects on which Leibniz and Descartes have divergent views.