Knowing how much good an outcome contains tells you nothing about who should have it, and knowing which acts are forbidden tells you nothing about how a society should be arranged.
That gap is where a third source of moral requirement sits. Its idea is that morality is what could be justified to each person affected, and that a principle nobody could reasonably refuse has an authority that neither a sum nor a commandment has. Contract theories of this kind have dominated political philosophy since 1971, and they answer objections the first two families could not: the separateness of persons, the limits of aggregation, and the question of why anyone should accept a rule at all.
The original position
John Rawls's A Theory of Justice in 1971 asks a question with a built-in answer to the problem of bias. What principles would free and rational people choose to govern the basic structure of their society, if they had to choose without knowing who in it they would be?
The veil of ignorance specifies what is removed. The parties do not know their class or social position, their race or sex, their natural talents and intelligence, their conception of the good life, their psychological dispositions, or the generation into which they are born. They do know general facts: economics, psychology, the circumstances under which societies function.
The device is not a story about a historical contract, and Rawls is explicit that no such agreement ever occurred. It is a representation of fairness. Anything you would agree to without knowing your position is something you cannot have chosen because it favours you, so the constraint models impartiality by information rather than by an appeal to benevolence. The parties are stipulated to be mutually disinterested, each caring only about their own share, which is deliberate: if the argument works with self-interested parties, it does not depend on anyone being good.
The choice is over an index of primary goods: rights and liberties, opportunities, income and wealth, and the social bases of self-respect. These are things a rational person wants whatever else they want, which lets the parties choose without knowing their conception of the good.
The two principles
Rawls argues that the parties would choose two principles, in a strict order of priority.
The first: each person has an equal claim to a fully adequate scheme of equal basic liberties, compatible with the same scheme for all. The second, applying to social and economic inequalities: they must attach to positions open to all under fair equality of opportunity, and they must be to the greatest benefit of the least advantaged members of society.
That last clause is the difference principle, and it is the famous one. It does not require equality. It permits any inequality that makes the worst-off group better off than they would be under a more equal arrangement, so a surgeon may earn many times a cleaner's wage if the incentive produces surgeons whose existence benefits cleaners. What it forbids is inequality that merely benefits the already advantaged.
The priority ordering is strict, which readers often miss. Liberties may not be traded for economic gain at all, not even a large one, and fair equality of opportunity takes priority over the difference principle. A society cannot buy prosperity for its poorest by disenfranchising a minority, however good the arithmetic.
Rawls's argument that the parties would choose this is that they would reason by maximin: rank the alternatives by their worst outcomes and choose the one whose worst outcome is best. He does not claim maximin is generally rational. He claims it is rational under three specific conditions, all of which the original position satisfies: there is no basis for assigning probabilities to the outcomes; the guaranteed minimum under maximin is satisfactory, so there is little to gain from gambling for more; and the alternatives contain outcomes the chooser could not accept, which he calls the strains of commitment, since a person who agreed to a principle and then found themselves crushed by it would not be able to keep the agreement.
Example. Three social arrangements give these welfare levels to three equally sized groups: A gives (10, 10, 10), B gives (5, 20, 20), C gives (8, 12, 40). Which does maximin choose, and which does an expected utility maximiser behind the veil choose?
Maximin compares worst outcomes: 10 for A, 5 for B, 8 for C, so it chooses A. An expected utility maximiser who assigns equal probability of being in any group compares averages: A gives 10, B gives , and C gives , so it chooses C. This is exactly John Harsanyi's objection, made in the 1950s before Rawls's book and pressed against it afterwards. Harsanyi argued that a rational chooser ignorant of their identity should assign equal probability to being anyone and maximise expected utility, which yields average utilitarianism rather than the difference principle, and that maximin is irrationally cautious: it would forbid crossing a road, since the worst outcome is death. Rawls's reply is that the original position is a choice about the terms of one's whole life made once and irrevocably, with no probabilities available and no chance to recover from a bad draw, so ordinary gambling reasoning does not apply. Which of the two is right is the central technical dispute about the argument, and it is unresolved.
Now you. Does the difference principle require the surgeon's high salary to be abolished?
Answer
Only if abolishing it would leave the worst-off group better off, which is an empirical question rather than a matter of principle. If high pay is what recruits and trains surgeons, and the worst-off benefit from having surgeons, the inequality is justified by the principle rather than tolerated in spite of it. If the pay is a rent extracted through a licensing monopoly, and the same supply of surgeons could be had for less with the savings going to the worst-off, the principle condemns it. This is worth noting because the difference principle is often described as egalitarian in a levelling sense, and it is not: it is indifferent to inequality as such, and cares only about the position of the bottom. That indifference is itself criticised from the left, by philosophers who hold that large inequalities are objectionable in themselves because of what they do to relations between citizens, and from the right by those who deny that the worst-off group's position is the right thing to maximise at all.
Nozick's answer
Robert Nozick's Anarchy, State, and Utopia, published three years later in 1974, is the most effective attack on the whole approach, and it works by changing the question.
Rawls asks which distribution is just. Nozick denies that justice is a property of distributions at all. On his entitlement theory, a distribution is just if it arose by just steps: justice in acquisition, covering how unowned things come to be owned; justice in transfer, covering voluntary exchange and gift; and rectification, covering what to do about past violations. Whatever pattern results from just steps is just, however unequal, and no pattern is required.
His argument is the Wilt Chamberlain case, and it is worth working through. Suppose your favourite distribution, whatever it is, obtains: call it . Chamberlain, a basketball player people want to watch, signs a contract giving him 25 cents from each ticket, and a million people freely pay to see him play, each knowing where their quarter goes. He now has dollars, far more than anyone else, and the distribution is . Everyone in was entitled to what they held, everyone transferred voluntarily, nobody was worse off than they chose to be. If was just and every step was legitimate, how can be unjust? And if it is unjust, then maintaining any pattern requires continuously forbidding people from doing what they wish with what is theirs.
Nozick draws the conclusion sharply: taxation of earnings from labour is on a par with forced labour, since it takes a portion of what a person's hours produced without their consent.
The replies are strong and none is decisive. The step Nozick spends least effort on is acquisition, and it is where the theory is most vulnerable: nearly all existing holdings trace back through conquest, enclosure and slavery rather than through legitimate first acquisition, so his own principle of rectification would license redistribution on a scale that dwarfs anything Rawls proposes. The Lockean proviso he accepts, that acquisition must leave enough and as good for others, is hard to satisfy for land and impossible for a finite planet. And the case understates the background: the spectators' quarters buy entertainment in a society whose stadiums, contract law and policing they did not individually consent to either, so the picture of a distribution disturbed only by free choices is idealised.
Example. Which premise of the Chamberlain argument does a Rawlsian deny?
Not that the transfers were voluntary, and not that was just. What a Rawlsian denies is the framing: the difference principle applies to the basic structure of a society, its constitution, property system, tax rules and institutions, and not to individual transactions within it. Rawls is explicit about this. So the just arrangement is one in which the rules of property and taxation are set so that inequalities work to the benefit of the worst off, and within those rules people spend their money as they wish, including on basketball. Chamberlain's earnings are then taxed under a scheme chosen behind the veil, and nobody is being interfered with in any objectionable sense, since the tax was part of the entitlement all along rather than a subtraction from it. Whether that reply works depends on whether the distinction between the structure and the transactions can be sustained, which Nozick denies and which is the real point of disagreement. It is a much more interesting dispute than the one about whether people may pay to watch basketball.
Now you. Nozick says taxation of earnings from labour is on a par with forced labour. Test the analogy.
Answer
The analogy holds at one point and fails at several. It holds in that both take the product of hours worked without the worker's individual consent, which is the feature Nozick is pointing at, and a reader who dismisses it out of hand has not engaged with it. It fails on control: a forced labourer is told what work to do, for whom, and when, while a taxpayer chooses their occupation, their hours, and whether to work at all, and may reduce the tax to nothing by reducing the work. It fails on exit: emigration is available and slavery has no equivalent. And it assumes what it needs to prove, since calling the pre-tax wage the worker's own presupposes that the property and contract rules producing that wage are themselves prior to the tax system, when they are all part of one legal arrangement that no individual consented to either. That last objection, made by Liam Murphy and Thomas Nagel among others, is the strongest, and it does not show that high taxation is just. It shows that the question cannot be settled by pointing at a pre-tax number and calling it yours.
Scanlon and reasonable rejection
T. M. Scanlon's What We Owe to Each Other in 1998 takes the contract idea in a different direction, aiming at interpersonal morality rather than at the structure of society.
His formula: an act is wrong if it would be disallowed by any principle for the general regulation of behaviour that no one could reasonably reject as a basis for informed, unforced general agreement.
Two features carry the weight. The motivation is not self-interest but the desire to justify oneself to others on terms they could not reasonably refuse, which Scanlon takes to be a basic and widely shared concern. And rejection is individualist: a principle can only be rejected by a person, on the ground of the burden it places on them, and complaints may not be summed across people. Many small burdens spread over a large number of people do not add up to one big complaint, because there is nobody who bears the sum.
The individualist restriction is what makes the theory a genuine rival to consequentialism, and Scanlon's illustration is the transmitter room. A technician, Jones, is trapped under fallen equipment where he is receiving painful electric shocks. We can rescue him, but only by interrupting a transmission of a football match being watched by millions of people, who will be mildly disappointed. Aggregating says the millions win, since enough small disappointments outweigh fifteen minutes of agony. Scanlon says they cannot: each viewer's complaint is trivial, no viewer bears a burden anywhere near Jones's, and no number of trivial complaints becomes a serious one.
The theory then faces the opposite problem, which is that numbers sometimes obviously do count. If you can save one person on one island or five on another, and all six face the same death, everyone thinks you should save the five, yet each of the five has exactly the complaint the one has, and no complaint is greater. John Taurek argued in 1977 that this shows the numbers should not count, and that you should flip a coin. Scanlon's reply is a tie-breaker argument: a principle that ignored the additional people would be reasonably rejectable by them, because it would treat their presence as making no difference at all, which is a failure to count them rather than a refusal to add them up. Whether this genuinely avoids aggregation is disputed, and Parfit argued that it does not.
Example. Assess the transmitter room case on each of the three families of theory.
A consequentialist compares aggregate welfare: fifteen minutes of severe pain against millions of small disappointments, and if the audience is large enough the arithmetic favours leaving Jones, which almost everyone finds monstrous. A Kantian says Jones is being used as a means to the audience's entertainment, since his suffering is being permitted for their benefit on a plan he could not consent to, and rescues him. A contractualist says the same and explains why more precisely: the principle "interrupt transmissions to prevent serious injury" cannot be reasonably rejected by any individual viewer, since no viewer's burden is remotely comparable, while the principle that leaves Jones there can be reasonably rejected by him. Notice that the second and third agree on the verdict for different reasons, and that the contractualist reason generalises better: it explains not only why Jones should be rescued but why the size of the audience is irrelevant, which is the feature the case was designed to isolate.
Now you. Is it reasonable to reject a principle permitting a national speed limit of 130 kilometres per hour, given that a lower limit would save lives?
Answer
Probably not, and the reasoning shows the theory doing real work rather than delivering an obvious answer. The person harmed by the higher limit is someone who will die in a crash that a lower limit would have prevented, and their complaint is as serious as a complaint gets. The person burdened by a lower limit loses time, which is a much smaller burden. On a naive reading of the individualist restriction, the fatal complaint always wins and the limit should be as low as is compatible with movement, which nobody believes. Scanlon's answer is that the comparison is between generic reasons available to anyone occupying a position, assessed ex ante, and that everyone is both a potential victim and a potential traveller. Assessed that way, the question becomes whether a person, not knowing which they will be, could reasonably reject a limit at a given level, and the answer varies with the risk: a limit of 200 is rejectable, a limit of 30 on a motorway is rejectable by everyone whose life is consumed by travel, and somewhere between them a range of defensible limits sits. The example is a good test of whether you have understood the theory, because it shows that the individualist restriction is not a rule that the worst-off complaint automatically wins.
What contract views cannot reach
Every theory in this family shares one structural limitation, and it falls on the same people each time.
A contract is an agreement among parties who can make agreements. Rawls's parties are described as roughly equal in power and capable of contributing to a scheme of cooperation, which is what makes cooperation mutually advantageous and gives everyone a reason to be in the agreement. That construction has no place for anyone who cannot contribute or reciprocate: people with severe cognitive disabilities, non-human animals, and future generations, who cannot bargain with us because they do not exist yet and can do nothing for us in return.
Rawls saw this and set the problem aside, treating the severely disabled as a case for later and handling generations by a separate device, a just savings principle, which the parties adopt on the assumption that they do not know which generation they belong to. Nussbaum, in Frontiers of Justice in 2006, argues that the omissions are not incidental but structural, and that a theory grounded in mutual advantage between roughly equal parties can never be repaired to include those who bring nothing to the bargain. Her alternative, the capabilities approach, grounds entitlements in what a creature needs to live a life worthy of its dignity, which requires no reciprocity at all.
Scanlon's version has the same shape and a narrower version of the problem, since reasonable rejection requires a being capable of being given reasons. He addresses it by extending trusteeship: those who cannot reject principles for themselves are represented by those who can, which handles the severely disabled and infants at the cost of making their standing derivative.
This is worth holding beside the previous lesson. Contractualism gets the limits of aggregation right, which consequentialism cannot, and gets the boundary of the moral community wrong in precisely the place where sentience-based views get it right. No single theory has both.
Comparing the three on one case
Suppose a state is deciding whether to fund an expensive treatment that would extend the lives of a small number of people with a rare disease, at a cost that would otherwise fund routine care for many.
A consequentialist compares quality-adjusted life years bought per pound and funds whichever buys more, which will usually be the routine care, and treats the identity of the patients as irrelevant. Rawls's framework asks about the basic structure rather than the individual decision, and would generate a right to a fair share of health resources whose content is settled by what parties behind the veil, not knowing whether they would have the rare disease, would accept. Nozick's framework denies the state should be running the health service at all, and treats the question as one for the patients and whoever chooses to help them. Scanlon asks whose complaint is greater: the patient who dies without treatment has a serious one, and so does each patient denied routine care, and the answer depends on comparing those two burdens person by person rather than in aggregate, which is why contractualist reasoning tends to favour treating identified serious conditions more than a straight efficiency calculation does.
Each framework is doing something the others are not, and the disagreement is traceable to a single feature of each. That traceability is the point of the whole exercise, and the last part of this course puts it to work on the cases where people actually disagree, starting with the oldest and hardest of them.