What makes something fair? The question can be asked in a laboratory, on a playing field and in a courtroom, and it can be asked of babies. Infants as young as 12 months expect resources to be divided equally between two characters in a scene. A study of 15-month-old infants found that they could identify unequal distributions of food and drink, and that this sense of fairness was connected to their own willingness to share. Even infants as young as 15 to 16 months tend to prefer interacting with individuals they have seen behaving fairly. By preschool, children will protest getting less than their peers, even paying to prevent the peer from getting more. Children apply a strong sense of fairness to others as well as themselves: in one set of studies, children chose to pay so they could stop a selfish child from getting away with unfair behavior. In a 2013 study, Shaw and Olson report that by age 3 to 4, children share equally with third parties when they can, and that by age six children dislike those who share unequally.

In a 2013 study, Shaw and Olson found that children use the value of resources, not just their number or size, when trying to make outcomes equal. Researchers who asked hundreds of children to share stickers found that older children seemed to think more explicitly about fairness norms when sharing cost them something, while younger children seemed more preoccupied with their own desires. Young children are aware of fairness norms and see them as applying to themselves, but the weight these norms carry may increase as children get older. Shaw and Olson (2013) note that children are perfectly willing to share unequally by giving more to the person with fewer resources, and they report that 6- to 8-year-olds are more concerned with making the outcome of a resource distribution equal. A child can keep a few special things just for themselves, and does not have to share everything.

Rewards raise a second question. Young children understand that someone who worked harder may deserve more reward. Young children often prefer to hand out rewards equally, even when one person worked harder. Children expect people who do equal work to share the reward equally. Children will sometimes give up their own reward to keep things even with another child. In a study of preschool-age children and others, the four-to-five-year-olds were the ones most likely to prefer that both rewards and punishments be distributed equally, while older children and adults preferred equitable allocations. When asked how to reward a hard worker and a slacker, the most common response from preschoolers was to give one cookie to each.

Is a sense of fairness the same everywhere? In a study of seven societies, children in every one would give up a food reward to stop a peer from getting more. In the same study, children in only three places (the U.S., Canada and Uganda) showed a dislike of getting an unfair advantage, at about age 9 or 10. Pairs of children in seven societies were randomly put in a disadvantageous or advantageous position; children rejected the disadvantageous position as early as age four and as late as age 10. Researchers on the seven-society study noted that earlier research suggested Western societies tend to emphasize equality, and that children in non-Western societies tend to share more than their peers in the West. A study of 15 small-scale societies using ultimatum, public goods and dictator games found that the standard model based on self-interest failed in all of the societies studied.

Scientists have tested animals too. Capuchin monkeys in experiments reacted badly to getting a less-favored reward when a partner got a better one. In a 2003 Emory study, capuchin monkeys given cucumber for a token trade completed 95 percent of trades when partners also got cucumber, but only 60 percent when partners got grapes. The monkey effect was amplified when the partner did not have to work for the reward; in that test the completed exchange rate fell to 20 percent, while the food-control test gave 55 percent. In a 2016 PLoS One study, dogs refused to continue giving their paw when only their partner was rewarded.

Here is a question: how should two people split a cake? In “I cut, you choose,” the other person picks the slice they like best, so neither person envies the other. Cake is not the same all the way through, so two pieces of the same size can be worth different amounts to different people. In Brams's view, a division should be considered fair only if two people think they both got pieces of the same value. In another method described by Science News Explores, each friend says where they would cut and someone else divides the middle section between them. University of Northern Iowa course notes say the cutter in “you cut I choose” divides the cake into two portions he sees as equal, but if the chooser’s preferences are known, the advantage shifts to the cutter. Quanta Magazine notes that envy-freeness is just one of several competing notions of fairness, and that a procedure achieving one will not necessarily achieve the others. Quanta Magazine concludes that in each case it is up to the individuals involved to decide if fair’s fair.

Some choices are left to chance. Casting or drawing lots has been used for thousands of years to deal with uncertainty and ensure fairness, and lotteries have been accepted as a fair, democratic way of making difficult choices. In soccer and in the NFL, the referee flips a coin before the game to decide who gets the first choice. Before a football game, the captain announces heads or tails before the referee flips the coin; the toss decides who gets first choice of receiving the kickoff or which goal to defend. Under the Laws of the Game for soccer, the referee tosses the coin, and the team that wins the toss decides which goal to attack in the first half or to take the kick-off; it must be the referee who tosses it. In a majority vote, the choice with the most votes decides the outcome. After a vote, someone may be unhappy with the result; that is part of voting.

Sports have a name for fairness: fair play. Fair play is deeply rooted in the Olympic ideal and sits at the heart of sports ethics. In the Olympic Oath, athletes swear that they have prepared themselves ethically and will keep to the rules. Fair play extends beyond following written rules to respecting unwritten rules, and includes unconditional respect for opponents, fellow players, referees and fans. Jim Parry argues that the rules function as a kind of pre-competition agreement which specifies an athlete’s eligibility to compete.

Next comes the idea of justice. The Roman emperor Justinian's definition of justice is the constant and perpetual will to render to each his due. In Aristotle's flute example, if there are fewer flutes than people who want to play them, they should go to the best performers; justice involves proportional treatment. Philosophers say goods can be shared according to a relevant criterion such as equality, desert or need, and that equality is the default principle in the absence of any special claims. David Hume argued that justice was to be understood as adherence to a set of rules that assign physical objects to individuals. A long-held principle of justice is that no man should profit by his own wrong, and that each person must take responsibility for his own conduct.

John Rawls set out justice as fairness in systematic detail in his 1971 book, A Theory of Justice, and called justice the first virtue of social institutions. Rawls asked people to imagine sitting behind a veil of ignorance that keeps them from knowing who they are, so that arbitrary facts do not influence the agreement. Ethics Unwrapped says that by being ignorant of our circumstances, we can more objectively consider how societies should operate. Rawls described the original position as a thought experiment in which each citizen is represented only as a free and equal citizen. Under Rawls's difference principle, social goods are to be distributed equally unless an unequal distribution would be to everyone's advantage; equality is the baseline. In Rawls's view, inequalities are to be to the greatest benefit of the least-advantaged members of society.

Magna Carta’s Clause 39 says no free man is to be arrested or imprisoned except by the lawful judgment of his peers or by the law of the land. An Australian rule-of-law explainer describes Magna Carta as a first step toward equality before the law, where no one, not even the King, was above the law. The explainer says those in power, including judges, police and lawmakers, must treat people equally and not make arbitrary distinctions. The Fourteenth Amendment says no state may deny any person the equal protection of the laws or deprive anyone of life, liberty or property without due process of law. The Preamble to the U.S. Constitution lists establishing Justice among its goals, and the Constitution says crimes shall be tried by jury. In a 2021 video, federal judges said they are not beholden to any one group and discussed their commitment to impartiality, the Constitution and the rule of law.

The Sixth Amendment trial right concerns an impartial jury, also known as a jury of your peers. Courts have a picture for fairness: Lady Justice. In the late 1400s, artists began to portray Lady Justice with a blindfold, but the blindfold was meant to be sarcastic. Lady Justice is often shown with a sword for the power of the law and with scales for two sides of an argument and eventual balance and justice. In the Illinois Supreme Court Building, Lady Justice appears with her eyes uncovered.

Words to know

• arbitrary: without fair reason
• impartiality: not taking sides
• norms: shared rules
• envies: wants theirs