All normative ethical theories, in some sense, assume that moral agents are rational agents.  To put it another way, it is assumed that moral acts should be supported by generally accepted reasons.

While the presence of rationality in moral discourse is explicit in some normative theories – for example, Immanuel Kant’s deontological moral theory, which derives morality from reason, claims that moral requirements are based on a standard of rationality (the categorical imperative), and delineates the community of moral agents as the ‘kingdom of rational agents,’ – it is nevertheless present as an assumption of other normative ethical theories as well.

Aristotle, for instance, famously wrote that human beings are ‘rational animals’ as such, virtue and living virtuously involve reason.  Aristotle writes: “we take the human function to be a certain kind of life, and take this life to be the soul’s activity and actions that express reason. Hence, the excellent man’s function is to do this finely and well.” (Nicomachean Ethics).

Utilitarianism also assumes rationality, trusting that moral agents are sufficiently rational to accurately predict the consequences of their actions, deliberate rationally, and on the basis of those rational processes, arrive at and act on the morally appropriate decision.

Moreover, we tend to think that those who are not fully rational have diminished moral responsibilities, that is, they are not moral agents.  We do not hold infants and children to blame, for example, when they fail to act appropriately in what are, for adults, moral situations.  Hence, a child is not blamed or held responsible for failing to rescue a person in distress.  Since the child is not fully rational, the child is not a moral agent.Rational

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