Ethics defines a few principles that bound morality. Among these is the axiom “ought implies can.” Moral responsibility ends where capability ends. This principle affirms that one is never expected to do the impossible even though our feelings of guilt or regret may indicate otherwise. One cannot demand and should forgive someone who fails to keep an obligation due to circumstances beyond their control.

Usually, “ought implies can” appears in arguments about the limit of moral responsibility. A person is morally obligated only to the extent fulfilling the obligation is possible. One may have a moral duty to pull someone away from a ledge before they fall, but one does not have a duty to fly into the air to rescue someone already falling. On the other hand, increased capability implies an correspondingly elevation of moral responsibility. The more one can do, the more one should do.

While ethicists generally agree that one is not obligated to accept harms to themselves in order to do good, luck egalitarians argue that people have an obligation to use their natural talents or accidental advantages to benefit others. Assuming that some people simply find themselves in advantaged situations or in possession of inborn talents, those people have an obligation to make themselves worthy of those gifts. By taking on that obligation, naturally advantaged people redistribute their good fortune, using it to help others. They become morally obligated to do so because of their capability and the circumstances that bestowed them.

As such, one might conclude that circumstance also informs capability from a moral perspective. Much like natural talents, an agent cannot control happening upon a situation in which some good needs to be done. If an agent sees an injured person while on a walk, and there does not appear to be any assistance on the way, the agent should act on the moral duty to prevent harm. If the agent recognizes that moral duty, they have an on-going obligation to watch for potential harms insofar as they are capable. Where multiple agents recognizing this duty are in the same situation, any one may abstain from intervening as long as at least one takes up the duty to prevent. Where one is alone, one must assume that duty oneself. Circumstance and ability may position an agent to be the sole possible candidate for accepting a moral duty. In such cases capability and circumstance bestow the obligation.

Collective action problems can arise when multiple agents who agree on the scope of moral duties all recognize an opportunity to enact their duty that can fulfilled by any one of them. If all agents involved wait for another to act, the situation may pass without fulfilling the duty. These issues can be mitigated if one also considers bias to action a component of moral duty. A moral duty defines an action to be performed, so the normative force of the obligation must likewise motivate an agent to respond to the duty with action unless another agent has already done so. In other words when an agent finds themselves looking for someone else to do something, they should then accept that the duty falls to them and take action.