This illustrates both the strengths and the limitations of ethics of duty.
This approach effectively counters a specific kind of evil—one that seeks to justify immoral actions by claiming they are consistent with duty. It appears powerless, however, against a second type of evil: one that openly acknowledges its immoral actions to be contrary to duty, but asserts that duty itself has no value, and that what is truly valuable is disregarding duty in pursuit of one's own interests.

An ethics of duty successfully demonstrates that the concept of duty is coherent and cannot be reduced to happiness or pleasure, thereby preventing those who commit immoral acts from invoking duty as a justification. It is powerless, however, against those who appeal to an alternative concept—such as value—to judge and ultimately dismiss the notion of duty.

This criticism applies to all ethics of duty, that is, to all moral doctrines that understand the foundation of morality as consisting in demonstrating that duties exist, or that commonly accepted moral rules are genuine duties.

The failure of ethics of duty does not necessarily entail the failure of moral theory as a whole; perhaps a different approach, one that assigns a different meaning to morality, might afford a clearer account of its foundations. Could we suggest that morality, rather than being concerned with the determination of duty, is instead a search for what brings us happiness?

2/ It Is Not Looking for What Makes Us Happy

The question of the foundation of morality can take on a meaning quite different from that of investigating whether duties exist. From an entirely different perspective, we might consider that founding morality means demonstrating that it enables us to attain happiness.

We will refer to doctrines that take this view as 'ethics of happiness'—and once again, we will not attempt to determine whether utilitarianism, which naturally comes to mind, falls under this heading.

Ethics of happiness can effectively demonstrate that happiness is what human beings prefer, and may even argue that the very essence of duty is bound up with happiness or pleasure. However, evil may take the form of an axiological position asserting that what has true value is the disappearance of humanity and all human desires, including the fundamental desire for happiness. The fact that human beings wish to be happy—or even that happiness is their deepest desire—does not allow us to infer that human existence itself has any inherent value.

Ethics of happiness thus suffers from the same flaw as ethics of duty: it can only counter certain forms of evil. It can counter egoism, by arguing effectively that what benefits me most is for all people to be happy—so that in pursuing my own happiness, I must also promote the general happiness of humanity.

Yet while it may succeed in refuting egoism, it cannot meet a second kind of evil: one that acknowledges my happiness depends on the happiness of others, but asserts that true value lies in the destruction of that happiness, and of humanity itself.