A law student at the beginning of his studies should know from where "ius" comes.  Its name is taken from justice.  For, in the elegant words of Celsus, "ius" is the art of the good and the equitable.  Consequently we jurists are called priests because we cultivate justice,  and we seek knowledge of the good and the equitable.  We mark the difference between equitable and inequitable and determine what is licit and not licit.  Iuri operam daturum prius nosse oportet, unde nomen iuris descendat. est autem a iustitia appellatum: nam, ut eleganter Celsus definit, ius est ars boni et aequi. Cuius merito quis nos sacerdotes appellet: iustitiam namque colimus et boni et aequi notitiam profitemur, aequum ab iniquo separantes, licitum ab illicito discernentes.  Justinian, Digest 1.1.1.1 (533 A.D.)  Ulpian on the First Book of the Institutes (ca. 230 A.D.)

Ambrogio Lorenzetti, Bad Government, Palazzo Pubblico, Siena,  1340 A.D.

The human race is ruled by two things, namely natural law and custom.  Natural law is what is contained in the law and the Gospel.  By it each person is commanded to do to others what he wants done to himself and prohibited from inflicting on others what he does not want done to himself.  So Christ said in the Gospel: "Whatever you want men to do to you, do so to them (Matthew 7:12)." Humanum genus duobus regitur, naturali uidelicet iure et moribus. Ius naturae est, quod in lege et euangelio continetur, quo quisque iubetur alii facere, quod sibi uult fieri, et prohibetur alii inferre, quod sibi nolit fieri. Unde Christus in euangelio:  "Omnia quecunque uultis ut faciant uobis homines, et uos eadem facite illis." Gratian, Prologue to his Decretum, ca. 1135.  Pacem in terris Justice is the constant and perpetual will to render to every man his due. Jurisprudence is the knowledge of divine and human affairs and knowledge of what is just and what is unjust. Iustitia est constans et perpetua voluntas ius suum cuique tribuens.  Iuris prudentia est divinarum atque humanarum rerum notitia, iusti atque iniusti scientia.    Justinian, Institutes 1.1 (533 A.D.)

 

What is justice but a tacit covenant of nature established for the aid of many.  Justice is not based on our statute but is a part of divine law and the bond of human society. Quid est iustitia, nisi naturae tacita conventio, in adiutorium multorum inventa. Iustitia non nostra constitutio, sed divina lex est, vinculum societatis humanae.

St. Martin of Braga, Formula honestae vitae (ca. 550 A.D.)

The Dying Barbarian, Greek, 2nd Century BC, Rome, Capitoline Museum

La Calunnia by Sandro Botticelli (ca. 1497)

Justice is the conformity of our actions and our will to the law.   Charles Bonaventure Marie Toullier (1752-1835)  Le droit civil français suivant l'ordre du code. Justice:  Proper administration of the laws.  In jurisprudence the constant and perpetual disposition of legal matters or disputes to render to every man his due.  Black's Law Dictionary (6th edition, 1990)
Distributive Justice

The obligations of the community to the individual

 

Commutative Justice

Obligations between persons that requires equality in all dealings between two persons.