Rule of JUSTICE

Perelman & Olbrechts-Tyteca introduce the rule of justice as a basic argumentative principle: “All beings of the same category must be treated in the same way”.
The rule is illustrated by some categories that have historically governed the distribution of benefits, “to each according to his merit; to each according to his birth; to each according to his needs” (Perelman [1963], p. 26).

The rule underlies claims such as “equal pay for equal work”. It involves the following operations.

(1) A categorization — First, individuals are categorized as members of a general category, “to be born”; “to have needs”; “to have merit” (admitting that one can deserve a punishment and that to have demerit is to have negative merit); “to be an employee, having worked such and such hours and produced such and such valuable products”.
General rights and duties can be defined with reference to this first level, “all human beings have the same right to life”. The following practice refers to a strict a pari argument, referring to thieves as a non-hierarchical category, “a thief is a thief”.

General Baclay was also quite a character, but a funny woman, very just in her own way. She shot women and men alike, all thieves, whether they stole a needle or an ox. A thief is a thief and they were all shot. It was just.
Ahmadou Kourouma, Allah is not obligated. 2000.[1]

(2) An equality relation and a hierarchy — Second, there is an equality relation defined as “equality of birth; of needs; of merits; of work”.
A hierarchy of individuals is derived from this relationship: “P has worked as much as Q or R …; more than A or B …; less than X or Y …”.

Such equipped categories can be represented on oriented scales. The position of an individual upon this scale can be discussed, “Does X has more/less merit than Y?”.
The metric is easy to define in cases of work, for example when it is determined by the weight of the fruit picked from the trees. Things get more complicated when it comes to scientific production, or when it comes to needs and merits. In any case, the criteria for giving priority to one person over another one must be established.

(3) A corresponding allocation scale — Another ranking method must be established in order to define the parallel scales of sanctions and rewards (what wages for that level of work?).
Then, the two scales must be coupled.

These two independent valuations ((2) and (3)) make the rule of justice more complex than an a pari argument. Gross a pari holds simply that “work must pay” – If P works, P has a right to be paid for that work (unless P is a volunteer working for a non-profit organization) – while the rule of justice connects two graduated scales.

Moreover, the rule of justice is assumed to be applied to all members of the group in a linear order. Actual rules include thresholds. For example, with respect to the level of taxation, the rule “to each according to his or her income” applies only above a certain threshold, and includes tax brackets and smoothing principles.

Other categories can be considered, showing that the rule of justice can be used to support injustice:

To each according to his or her sex
To each according to his or her color.

The rule of justice excludes arbitrariness, but not injustice. The rule of justice, according to the principle of “favor disfavor”, necessarily creates innumerable injustices. When the benefits are distributed according to merit, they are not distributed according to birth or need.
The rule of justice is said to be “just” because it excludes the arbitrariness of the principle “to each according to my convenience”; and because the categories with their corresponding hierarchy and the allocation scale have been defined by disregarding the cases to be judged, “the decision is just because the rule existed before your case. This “justice” is formally just because it allows the application of a legal syllogism.

[1] Ahmadou Kourouma, Allah n’est pas obligé. Paris: Le Seuil, p. 111