In his treatise on the Passions of the Soul , Descartes gave a fairly traditional description of gratitude ( reconnaissance ) and ingratitude. Gratitude is “a sort of love, excited in us by some action of him to whom we offer it, and whereby we believe he has done us some good, or at least had an intention to do us some. So it includes all that goodwill does, and this besides, that it is grounded on an action we are very sensible of, and whereof we have a desire to make a requital. Wherefore it is far more strong, especially in souls never so little noble and generous.”

Ingratitude is not a passion but a simple vice, an inversion of gratitude:

“For ingratitude ( ingratitude ), it is not a passion, for nature never put any motion of the spirits in us to excite it. But it is only a vice directly opposite to gratitude, seeing this is ever virtuous, and one of the principal bonds of human society. Wherefore this vice appertains to none but belluine men, and the foolishly arrogant, who think all things their due; or the sottish who reflect not on the good deeds they receive; or else the weak, and abject, who feeling their own infirmity and necessity, basely seek assistance from others, and after they have received it hate them because having no will to return the like, or despairing ever to do it, and imagining the whole world as mercenary as themselves, and that none do good but with hope of being rewarded for it, they think they have desired it.”

Kant too endorse gratitude, and insisted in the Metaphysics of Morals that it extended even to prior generations: Gratitude “reaches not only to one’s contemporaries but also to one’s predecessors, even to those one cannot identify with certainty. It is for this reason, too, that it is through improper not to defend the ancients, who can be regarded as our teachers, from all attacks, accusations, and disdain, insofar as this is possible. But it is a foolish mistake to attribute preeminence in talents and good will to the ancients in preference to the moderns just because of their antiquity, as if the world were steadily declining in accordance with laws of nature from its original perfection, and to despise everything new in comparison with antiquity.”

In continuity with traditional reflections on gratitude (Seneca and Thomas), Kant categorized gratitude as a kind of justice, an obligation due to someone who had done a favor. And he also discussed the spectrum of obligation that different favors might impose. Intensity of gratitude is proportionate to “how useful the favor was to the one put under obligation and how unselfishly it was bestowed on him. The least degree is to render equal services to the benefactor if he can receive them (if he is still living) or, if he cannot, to render them to others; it involves not regarding a kindness received as a burden one would gladly be rid of (since the one so favored stands a step lower than his benefactor, and this wounds his pride), but taking even the occasion for gratitude as a moral kindness, that is, as an opportunity given one to unite the virtue of gratitude with love of man, to combine the cordiality of a benevolent disposition with sensitivity to benevolence (attentiveness to the smallest degree of this disposition in one’s thought of duty), and so to cultivate one’s love of human beings.”