Key Ideas
The moral law is a “fact of reason”.
Freedom is the ratio essendi of the moral law; the moral law is the ratio cognoscendi of freedom.
The highest good unites virtue and happiness proportionately — which requires postulating God and immortality.
The book ends with the most famous paragraph Kant wrote — the “starry heavens above me and the moral law within me”.
Lines to Remember
1 quotationsTwo things fill the mind with ever new and increasing admiration and awe, the more often and steadily we reflect upon them: the starry heavens above me and the moral law within me.
Zwei Dinge erfüllen das Gemüt mit immer neuer und zunehmender Bewunderung und Ehrfurcht, je öfter und anhaltender sich das Nachdenken damit beschäftigt: der bestirnte Himmel über mir und das moralische Gesetz in mir.
Context & when to use it
The closing of the second Critique. The first “thing” humbles us — we are specks in an infinite cosmos; the second elevates us — as moral beings we stand outside the mechanism of nature. It is engraved on Kant’s tomb in Königsberg.
For wonder, for the dignity of conscience, or to answer anyone who says science has made morality small.
Explore Next
related by shared connectionsThe Categorical Imperative
Kant’s supreme principle of morality — act only on maxims you could will as universal laws; treat humanity always as an end, never merely as a means.
Critique of Pure Reason
Kant’s masterwork, asking what reason can know without experience — and answering that it can know the forms of all possible experience, but nothing beyond.
Existentialism Is a Humanism
Sartre’s 1945 public lecture — the most popular statement of existentialism — existence precedes essence, man is condemned to be free.
Jean-Jacques Rousseau
The Genevan philosopher of nature, freedom and feeling — “Man is born free, and everywhere he is in chains” — whose Social Contract inspired revolutionaries and whose Confessions invented modern autobiography.
Prolegomena to Any Future Metaphysics
Kant’s short, clearer restatement of the first Critique, where he credits Hume with waking him from his dogmatic slumber.
German Idealism
The extraordinary philosophical movement after Kant — Fichte, Schelling, Hegel — that tried to complete his revolution by showing reality itself to be the work of mind or Spirit.