A situation in which humans have to choose between two things that cannot be had at the same time

problem of moral responsibility, the problem of reconciling the belief that people are morally responsible for what they do with the apparent fact that humans do not have free will because their actions are causally determined. It is an ancient and enduring philosophical puzzle.

Historically, most proposed solutions to the problem of moral responsibility have attempted to establish that humans do have free will. But what does free will consist of? When people make decisions or perform actions, they usually feel as though they are choosing or acting freely. A person may decide, for example, to buy apples instead of oranges, to vacation in France rather than in Italy, or to call a sister in Nebraska instead of a brother in Florida. On the other hand, there are at least some situations in which people seem not to act freely, as when they are physically coerced or mentally or emotionally manipulated. One way to formalize the intuitive idea of free action is to say that a person acts freely if it is true that he could have acted otherwise. Buying apples is ordinarily a free action because in ordinary circumstances one can buy oranges instead; nothing forces one to buy apples or prevents one from buying oranges.

Yet the decisions a person makes are the result of his desires, and his desires are determined by his circumstances, his past experiences, and his psychological and personality traits—his dispositions, tastes, temperament, intelligence, and so on. Circumstances, experiences, and traits in this sense are obviously the result of many factors outside the individual’s control, including his upbringing and perhaps even his genetic makeup. If this is correct, then a person’s actions may ultimately be no more the result of free will than his eye colour.

The existence of free will seems to be presupposed by the notion of moral responsibility. Most people would agree that a person cannot be morally responsible for actions that he could not help but perform. Moreover, moral praise and blame, or reward and punishment, seem to make sense only on the assumption that the agent in question is morally responsible. These considerations seem to imply a choice between two implausible alternatives: either (1) people have free will, in which case a person’s actions are not determined by his circumstances, past experiences, and psychological and personality traits, or (2) people do not have free will, in which case no one is ever morally responsible for what he does. This dilemma is the problem of moral responsibility.

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Determinism is the view that, given the state of the universe (the complete physical properties of all its parts) at a certain time and the laws of nature operative in the universe at that time, the state of the universe at any subsequent time is completely determined. No subsequent state of the universe can be other than what it is. Since human actions, at an appropriate level of description, are part of the universe, it follows that humans cannot act otherwise than they do; free will is impossible. (It is important to distinguish determinism from mere causation. Determinism is not the thesis that every event has a cause, since causes do not always necessitate their effects. It is, rather, the thesis that every event is causally inevitable. If an event has occurred, then it is impossible that it could not have occurred, given the previous state of the universe and the laws of nature.)

Philosophers and scientists who believe that the universe is deterministic and that determinism is incompatible with free will are called “hard” determinists. Since moral responsibility seems to require free will, hard determinism implies that no one is morally responsible for his actions. Although the conclusion is strongly counterintuitive, some hard determinists have insisted that the weight of philosophical argument requires that it be accepted. There is no alternative but to reform the intuitive beliefs in freedom and moral responsibility. Other hard determinists, acknowledging that such reform is scarcely feasible, hold that there may be social benefits to feeling and exhibiting moral emotions, even though the emotions themselves are based on a fiction. Such benefits are reason enough for holding fast to prephilosophical beliefs about free will and moral responsibility, according to these thinkers.

The extreme alternative to determinism is indeterminism, the view that at least some events have no deterministic cause but occur randomly, or by chance. Indeterminism is supported to some extent by research in quantum mechanics, which suggests that some events at the quantum level are in principle unpredictable (and therefore random).

Philosophers and scientists who believe that the universe is indeterministic and that humans possess free will are known as “libertarians” (libertarianism in this sense is not to be confused with the school of political philosophy called libertarianism). Although it is possible to hold that the universe is indeterministic and that human actions are nevertheless determined, few contemporary philosophers defend this view.

Libertarianism is vulnerable to what is called the “intelligibility” objection. This objection points out that a person can have no more control over a purely random action than he has over an action that is deterministically inevitable; in neither case does free will enter the picture. Hence, if human actions are indeterministic, free will does not exist.

The German enlightenment philosopher Immanuel Kant (1724–1804), one of the earliest supporters of libertarianism, attempted to overcome the intelligibility objection, and thereby to make room for moral responsibility, by proposing a kind of dualism in human nature. In his Critique of Practical Reason (1788), Kant claimed that humans are free when their actions are governed by reason. Reason (what he sometimes called the “noumenal self”) is in some sense independent of the rest of the agent, allowing him to choose morally. Kant’s theory requires that reason be disconnected from the causal order in such a way as to be capable of choosing or acting on its own and, at the same time, that it be connected to the causal order in such a way as to be an integral determinant of human actions. The details of Kant’s view have been the subject of much debate, and it remains unclear whether it is coherent.

Treadmills were used in muscle-powered machinery since ancient times, and 19th-century English jails used them to punish prisoners.

Although libertarianism was not popular among 19th-century philosophers, it enjoyed a revival in the mid-20th century. The most influential of the new libertarian accounts were the so-called “agent-causation” theories. First proposed by the American philosopher Roderick Chisholm (1916–99) in his seminal paper “Human Freedom and the Self” (1964), these theories hold that free actions are caused by the agent himself rather than by some prior event or state of affairs. Although Chisholm’s theory preserves the intuition that the ultimate origin of an action—and thus the ultimate moral responsibility for it—lies with the agent, it does not explain the details or mechanism of agent-causation. Agent-causation is a primitive, unanalyzable notion; it cannot be reduced to anything more basic. Not surprisingly, many philosophers found Chisholm’s theory unsatisfactory. What is wanted, they objected, is a theory that explains what freedom is and how it is possible, not one that simply posits freedom. Agent-causation theories, they maintained, leave a blank space where an explanation ought to be.