The principles of equity, equality, and need are most relevant in the context of distributive justice, but might play a role in a variety of social justice issues.[4] These principles all appeal to the notion of desert, the idea that fair treatment is a matter of giving people what they deserve. In general, people deserve to be rewarded for their effort and productivity, punished for their transgressions, treated as equal persons, and have their basic needs met. However, because these principles may come into conflict, it is often difficult to achieve all of these goals simultaneously.

According to the principle of equity, a fair economic system is one that distributes goods to individuals in proportion to their input. While input typically comes in the form of productivity, ability or talent might also play a role. People who produce more or better products...either by working harder, or by being more talented, this argument goes, should be paid more for their efforts than should people who produce less. Note that this sort of distribution may not succeed in meeting the needs of all members of society.

In addition, the idea that justice requires the unequal treatment of unequals is in tension with the principle of equality. This principle of egalitarianism suggests that the fairest allocation is one that distributes benefits and burdens equally among all parties. If there are profits of $100,000, and 10 people in the company, the principle of equality would suggest that everyone would get $10,000. This principle, however, ignores differences in effort, talent, and productivity. Also, because people have different needs, an equal initial distribution may not result in an equal outcome.

A principle of need, on the other hand, proposes that we strive for an equal outcome in which all society or group members get what they need. Thus poor people would get more money, and richer people would get less. This principle is sometimes criticized because it does not recognize differences in productive contributions or distinguish between real needs and purported needs.

Some have suggested that equity, equality, and need are not principles adopted for their own sake, but rather ones endorsed to advance some social goal.[5] For example, while equity tends to foster productivity, principles of equality and need tend to stress the importance of positive interpersonal relationships and a sense of belonging among society members.