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Moral luck describes circumstances whereby a moral agent is assigned moral blame or praise for an action or its consequences even if it is clear that said agent did not have full control over either the action or its consequences. This term, introduced by Bernard Williams, has been developed, along with its significance to a coherent moral theory, by Williams and Thomas Nagel in their respective essays on the subject.
Broadly speaking, human beings tend to correlate, at least intuitively, responsibility and voluntary action. Thus, the most blame is assigned to persons for their actions and the consequences they entail when we have good cause to believe that both:
Conversely, there is a tendency to be much more sympathetic to those who satisfy any of the following conditions:
Parenthetically, the above criteria do not correlate exactly with moral praise - while it may be true that one can, and should assign a good deal of moral praise to those who had performed a good action, or an action entailing good consequences, completely on their own volition and uncoerced, it is debatable that the same distinction holds for involuntary actions that happened to turn out well or happened to produce good outcomes.
This correlation between responsibility and voluntary action is acceptable to most people on an intuitive level; indeed, this correlation is echoed in American and European law: for this reason, for example, manslaughter, or killing in self-defense carries a significantly different type of legal punishment (i.e., formalized moral blame) than premeditated murder.
Given the notion of equating moral responsibility with voluntary action, however, moral luck becomes a problem. This problem is illustrated by an example that many moral luck philosophers employ - that of a traffic accident.
There are two people driving cars, Driver A, and Driver B. They are alike in every way. Driver A is driving down a road, and, in a moment of inattention, runs a red light as a child is crossing the street. Driver A slams the brakes, swerves, in short does everything to try to avoid hitting the child - alas, the car hits and kills the child. Driver B, in the meantime, also runs a red light but, since no one is crossing, gets a traffic ticket but nothing more.
If a bystander were asked to morally evaluate Drivers A and B, there is very good reason to expect them to say that Driver A is due more moral blame than Driver B. After all, Driver A's course of action resulted in a death, whereas the course of action taken by Driver B was quite uneventful. However, there are absolutely no differences in the controllable actions performed by Drivers A and B. The only disparity is that in the case of Driver A, an external uncontrollable event occurred, whereas it did not in the case of Driver B. The external uncontrollable event, of course, is the child crossing the street. There is no difference at all in what the two of them could have done - however, one seems clearly more to blame than the other. How does this occur?
This is the problem of moral luck. If it is given that moral responsibility should only be relevant when the agent voluntarily performed or failed to perform some action, Drivers A and B should be blamed equally, or praised equally, as may be the case. At the same time, this is at least intuitively problematic, as - whatever the external circumstances are - one situation resulted in a death, and the other did not.
Thomas Nagel (1979) identified four kinds of moral luck in his essay. The kind most relevant to the above example is "resultant moral luck".
Resultant moral luck concerns the consequences of actions and situations. In the above example, both drivers were affected by resultant moral luck in that a particular set of circumstances turned out in two different ways: in one situation, a pedestrian appeared on the road; in the other, the pedestrian did not.
Circumstantial moral luck concerns the surroundings of the moral agent. The best-known example is provided in Nagel's essay. Consider Nazi followers and supporters in Hitler's Germany. They were and are worthy of moral blame either for committing morally reprehensible deeds or for allowing them to occur without making efforts to oppose them. But, if in 1929, those people were moved to some other country, away from the coming hostilities by their employers, it is quite possible that they would have led very different lives, and we could not assign the same amount of moral blame to them. It is down, then, to the luck of the circumstances in which they find themselves.
Constitutive moral luck concerns the personal character of a moral agent. There can be little argument that education, upbringing, genes and other largely uncontrollable influences shape personality to some extent. Furthermore, one's personality dictates one's actions to some extent. Moral blame is assigned to an individual for being extremely selfish, even though that selfishness is almost certainly due in part to external environmental effects.
Causal moral luck, which equates largely with the problem of free will, is the least-detailed of the varieties that Thomas Nagel describes. The general definition is that actions are determined by external events and are thus consequences of events over which the person taking the action has no control. Since people are restricted in their choice of actions by the events that precede them, they should not be held accountable or responsible for such actions.
Thomas Nagel has been criticized[by whom?] for including causal moral luck as a separate category, since it appears largely redundant. It does not cover any cases that are not already included in constitutive and circumstantial luck, and seems to exist only for the purpose of bringing up the problem of free will.
Some philosophers, such as Susan Wolf, have tried to come up with "happy mediums" that strike a balance between rejecting moral luck outright and accepting it wholesale. Wolf introduced the notions of rationalist and irrationalist positions as part of such a reconciliation.
The rationalist position, stated simply, is that equal fault deserves equal blame. For example, given two drivers, both of whom failed to check their brakes before driving, one of them runs over a pedestrian as a consequence while the other does not. The rationalist would say that since both of the drivers were equally at fault in failing to check their brakes, it should make no difference that one of them was lucky in not hitting a pedestrian while the other was unlucky - moral fault is independent of consequence. Since the fault here is equal, the agents should receive equal blame.
The consequentialist position argues that equal fault need not deserve equal blame, as blame should depend on the consequences. By this logic, the lucky driver certainly does not deserve as much blame as the unlucky driver, even though their faults were identical.
Wolf combines these two approaches in trying to reconcile the tensions associated with moral luck by introducing the concept of a virtuous agent. A virtuous agent should accept that they have a special connection with the consequences of their actions, including equal-fault cases (such as the lucky/unlucky drivers above), and even in no-fault cases. This argument essentially retains the rationalist claim that equal fault is equally deserving of blame while also retaining the consequentialist claim that different outcomes should result in moral agents feeling and acting differently.
It is important to underline the distinction between internal and external moral blame or praise. Wolf believes that the outsiders should blame the lucky and unlucky drivers equally despite their intuition that the two of them should not feel equally bad (i.e., the unlucky driver that ran over a pedestrian should feel worse). However, the unlucky driver themselves should voluntarily accept the notion of the special connection between their actions and the unfortunate consequences, and assign more blame to themselves than the lucky driver should.