Theorem: Both choices on benefit between the subject and others may be justice when benefits conflict and the total benefit is not able to rise or avoid to fall.

For example, there is only one champion in a sports competition. Whatever you choose it means someone has to sacrifice. At this time, whatever you choose is justice.

If the sum of benefits may increase, then one party needs to make sacrifice to achieve Paretian optimization. At this time, the choice of justice is to sacrifice the interests of someone in order to realize the greatest benefit.

Theorem: The maximization of benefit is justice when benefits conflict and the total benefit is able to rise or avoid to fall.

In many countries, efficiency is prioritized and fairness is taken into consideration. Efficiency here refers to the maximization of social benefits, not to the efficiency of a machine or a social organization.

Although it is difficult to calculate the sum of interests, people have been making such calculations and comparisons. For example, after the Vietnam War, Americans felt that national interests were overestimated and they no longer wished to sacrifice their own interests for national interests. But after “9.11”, Americans felt that national interests are very important and they were willing to pay more tax for the country's security. Each year, Congress's budget debates are mainly due to differences in the calculation of the sum of benefits.

It should be noted that the rule to maximize the sum of interests is not exactly the same as the rule that minority obeys the majority. For example, each person donates a little money to save a person's life, which is at the expense of the majority, but it is also to maximize the sum of interests, because the sum of the interests of the sacrificed majority is less than the individual's interest of that person.

When the influence of behavior on the interests of each individual is almost equal, the following inference can be derived from the above theorem:

Corollary: Benefit of majority is the criterion of justice, when benefits conflict and each one's change of benefit is almost the same.

There are three ways to sacrifice the interests of someone: by force, will or deal. Forcing someone to sacrifice is called struggle. If the goal of the struggle is to increase the total interest and meet the principle of justice, it is called the just struggle. If the total interest is reduced, it is called the unjust struggle. If the sum of interests is unchanged, this struggle does not matter justice and injustice, but it has good and evil. The struggle includes both force and peace. Human society is always inevitably struggling.

Conflicts can cause damages for both parties. To reduce this damage, people hope to find a choice acceptable to both parties. Sacrificing the interests of one party by means of transactions is to allow the beneficiaries to transfer part of the benefits to the victims. This kind of approach can turn interest conflict into benefits unity, which is the most ideal. But can not be realized in all conditions.