Compare and contrast Kant and Sartre. We may say that Sartre inverts Kant’s moral philosophy. What does Sartre share with Kant, and how does he overturn some of his thinking?
▻ THE CENTRALITY OF FREE AGENCY
In his Religion within the Limits of Reason Alone, Kant turns his attention to the problem of evil and, in doing so, develops a more complex picture of the human will and its moral character than is found in his earlier works. The discussion of radical evil - of how free beings can misuse their freedom ? rests on his notion of a freely chosen disposition. Imputability of our actions requires that we be the authors of this enduring aspect of the will. This description of our character, of our disposition, in short, of ourselves, as resulting from a free choice foreshadows existentialist themes developed by Jean-Paul Sartre; most notably, the fundamental project and the idea of radical choice. (Marcel Lieberman, 'The Limits of Comparison: Kant and Sartre on the Fundamental Project', History of Philosophy Quarterly, Vol. 14, No. 2 (Apr., 1997), pp. 207-217 : 207.)
Sartre rejects determinism, which he sees as inconsistent with radical choice and Kant rejects determinism at least as far as concerns human moral action.
▻ DIVERGENCE OVER HUMAN NATURE
Sartre famously affirms that our existence precedes our essence, by which he means that we first exist (are 'thrown into the world', as Heidegger says) and then define ourselves - acquire an essence - through and in authentic choice. In contrast Kant believes that we are essentially rational beings, bound rationally to certain rules of conduct (defined by the categorical imperative in its various formulations) to act in certain ways. Sartre holds and can hold no such idea of a blueprint of rationality by which we are defined and to which we have any obligation of any kind to conform.
▻ LEGISLATING FOR HUMANITY
Kant's ethics rests on the idea that in acting we should heed principles that can be universalised - principles on which everyone can act. Sartre holds a view not dissimilar :
When a man commits himself to anything, fully realizing that he is not only choosing what he will be, but is thereby at the same time a legislator deciding for the whole of mankind - in such a moment a man cannot escape from the sense of complete and profound responsibility. (J.-P.Sartre, Existentialism is a Humanism, in Walter Kaufmann (ed.) Existentialism from Dostoevsky to Sartre (Cleveland: Meridian Books, 1956), pp.297-8.)
Marcel Lieberman, 'The Limits of Comparison: Kant and Sartre on the Fundamental Project', History of Philosophy Quarterly, Vol. 14, No. 2 (Apr., 1997), pp. 207-217.
Thomas Baldwin, 'The Original Choice in Sartre and Kant', Proceedings of the Aristotelian Society, New Series, Vol. 80 (1979 - 1980), pp. 31-44
Wesley K. H. Teo, 'Self-Responsibility in Existentialism and Buddhism', International Journal for Philosophy of Religion, Vol. 4, No. 2 (Summer, 1973), pp. 80-91.