Autonomy is the capacity for self-government. Agents are autonomous if their actions are truly their own. The necessity of this moral liberty appears in Rousseau, and is a cornerstone of Kant's ethical theory, in which possessing autonomy of the will is a necessary condition of moral agency. The difficulty in the concept is that our desires, choices, and actions are all partly caused by factors outside our control, including those factors originally responsible for our characters. So true autonomy can easily seem to be a myth. Yet the concept is important, since it is plausible to hold that only agents acting autonomously are responsible for their actions. But this idea also leads to quicksands: autonomy is often contrasted with the state of being ‘enslaved’ by bad desires. But if only the autonomous can be held responsible it will quickly follow that nobody is responsible for bad actions. Proposals for defending the concept include describing agents as autonomous when they are under the influence only of reason, when they can identify with the motivations prompting their action, or when they are capable of acting so as to change their motivations if they cannot identify with them. Agents are heteronomous if their will is under the control of another. It should be noted that the pair is not exhaustive: an agent may fail to be autonomous because of external factors that do not include control by another, but only other kinds of constraint and compulsion.
In the ethics of Kant the terms are more specific. Autonomy is the ability to know what morality requires of us, and functions not as freedom to pursue our ends, but as the power of an agent to act on objective and universally valid rules of conduct, certified by reason alone. Heteronomy is the condition of acting on desires, which are not legislated by reason. The centrality of autonomy is challenged by ethical theorists, including many feminists, who see it as a fantasy that masks the social and personal springs of all thought and action. See also authenticity, determinism, free will, libertarianism (metaphysical).