Williams suggests that most ancient Greeks did not consider the question of whether slavery was just because they took it for granted that slavery was necessary for their way of life. Aristotle made an even stronger claim, which is that slavery is just because some people are naturally born slaves. Some people have a necessary identity as a slave. Not only do modern thinkers reject the notion that people are born with necessary identities; we also reject the idea that considerations of justice cannot be replaced by luck, fortune or fate. We cannot let luck settle questions of justice. In modern society, we set up social institutions like homeless shelters, job training and health care; these institutions help us to mitigate the effects of bad luck. The social or economic necessity that might make a person born poor remain poor, need not be coercive. This means that no individual person's luck will be worse than others'.
Williams thinks that even though we attempt to control luck, we can never be completely successful. Life is tragic and incomprehensible. Ancient Greek poets were aware of this fact about human life. Philosophers are guilty of trying to show that there is a rational order to the universe. Williams thinks that the philosophers are wrong and the poets are right. As evidence, it is a common occurrence in tropical places for people to be killed by falling coconuts. This is a seemingly absurd event. There is no rational explanation for such a death! We cannot make sense of it in terms of human purposes and human interests. There is no predictable pattern or "style" to supernatural necessity.
Supernatural necessity can be contrasts with human necessity. Human necessity is when one person forces another to do something, such as in the case of slavery. Supernatural necessity is beyond or behind human necessity. For example, a supernatural force may put a person in a situation to choose between two things that they care about. For example, if a man stranded on a desert island found a rescue boat which can only hold one other person. If this man has two children, he will have to choose one. One interpretation of this situation is to say that such a person is forced to make a choice but that the choice is still his. The man is not forced to choose a particular way. Is accepting one's fate heroic or is it weak?
When a person in an ancient Greek tragedy accepts her fate, is this heroic or is it caving in to fate? Is a person only accepting fate or collapsing in the face of fate? It is true that luck may be against you, but you never know in what way exactly. Once your fate has been determined, it is not only the case that things cannot be otherwise, but things will not be otherwise. It may be unclear why this is the case. We may not know how or why things must have been the way they are. It's also not relevant because the gods are in control. While human affairs might be explainable and understandable, this is not the case when the gods are in charge. We cannot apply rational explanations to the actions of the gods.
Even if our lives are not controlled by capricious gods, Williams thinks that this does not yet mean that we are free. The real obstacle to freedom is not a supernatural god. The real obstacles to freedom are psychological, social and political causes. For example, your parents or superiors at work can control you just as much as the gods could. In another example, the influence of your family life and education can control you just as much as fate. Even if our choices are not restricted, we can still be made unfree if we are persuaded by other people or forced to do things by other people. In a more extreme case, people can be brainwashed and thus lose their freedom. In many cases, not only are subjects of tyrannical governments made unfree; the tyrants themselves become controlled by their own brainwashing and rhetoric.
Kant and Plato object that people are free to determine themselves with reason when they are freed from outside influences. Aristotle thought that although we are all embedded in a society, we can still shape and guide ourselves with rationality. Hegel thought that our individual selves must be in harmony with social life. But the poets suggest that these ideas about self-control are illusions. The poets think that our lives are necessarily unharmonious. They think that we cannot make perfect sense of the world with human reason. The world is only partially intelligible.