  One of Descartes' first metaphysical first principles that he proves is the existence and nature (as benevolent) of God. His primary reason for this is to call upon a benevolent God as a guarantor of the truth of his clear and distinct ideas. Immediately after her discussion of her first principles of knowledge, Du Châtelet also turns to metaphysical first principles that can be derived from the epistemology, and she too turns to a proof for the existence and nature of God. But her reasons for doing so are different from Descartes' immediate reasons as just articulated. For Du Châtelet, as Marcy Lascano has rightly argued, “wanted to provide a ground for physics that would explain the rational basis of the workings of the universe. Proving that an eternal, good and rational being created the universe would provide such a ground” (Lascano 2011, 743). In Du Châtelet's words, “[t]he study of nature elevates us to the knowledge of the supreme being; this great truth is even more necessary, if possible, to good physics than to morality, and it ought to be the foundation and conclusion of all the research we make in this science” (IP §18, p. 138). As shown above, Du Châtelet believes in the interconnectedness and systematicity of the natural world as a whole, and she believes that this is a crucial general reason why God has chosen to actualize this world. And so, it seems humans do have cognitive access to this sufficient reason for why God chose this world as opposed to any other world. In fact, Du Châtelet links the interconnectedness and systematicity of the natural world as a whole with perfection (§26), thus indicating that God's sufficient reason for his choice of this world over any other possible worlds in a further principle, namely, the Principle of the Best. Du Châtelet's belief in the interconnectedness and systematicity of the natural world as a whole is the key to her method and physics, even though (as shown below) there are limits to the role that can be played in physics by these metaphysical features of the world. Nonetheless, establishing the existence of God as one who would choose to actualize such a world is Du Châtelet's next crucial step.