[In preparation for the conclusion of the Mansfield Park essay, I am posing this short note on a famous Kant's note where he explains Newton's and Rousseau's impact on his ethical thought. Here I reproduce J. B. Schneewind's translation and notes.]
[W]e can see one of the most frequently quoted of Kant’s notes as showing a problem of which he was plainly aware.
Newton first of all saw order and regularity unified with great simplicity where before him disorder and badly sorted multiplicity were to be met and since the comets run in geometric paths.
Rousseau first of all discovered beneath the multiplicity of forms assumed by humans their deeply buried nature and the hidden law by which providence through his observations will be justified. Previously the reproach of Alphonsus and Manes was valid. After Newton and Rousseau God is justified and now Pope’s theorem is true.
[Footnote] Alphonsus was a king of Castile who was an astronomer and who claimed that he could have given God some good advice about making the heavens more orderly. Leibniz among many others mentions his criticism of God in order to dismiss it in Theodicy [...]. Manes is the founder of the dualistic Manichaean religion. [... Schneewind explains in 22.iii that] Pope’s theorem as Kant read it is that whatever is, is good; it comes from his Essay on Man.
If Newton showed the hidden law revealing a divine order in the natural world, Rousseau did something anologous for the moral world: he explained the presenet disorder in the moral world of which his vicar complains so elequently, and did so in a way that shows it to be our fault, not God’s. But the only advice he offers for creating order seems to be the formation of the social contract. And that in turn seems to contradict the vicar’s insistence that morality must be something we each come to know individually, by looking within ourselves, regardless of book learning. Rousseau thinks that a legislator of God-like abilities is needed “to give laws to men”; he might have to pretend to have divine authority in order to convince the masses to obey (Oeuvres III.362-4, Contract II.vii). Rousseau no more tries to reconcile these claims than he tries to answer the vicar’s request for moral guidance.
J. B. Schneewin, The Invention of Autonomy, p. 491
Kant on Newton and Rousseau