The Catechism of the Summa - SECOND SECTION - A DETAILED SURVEY OF MAN'S RETURN TO GOD - XVII. OF JUSTICE AND ITS NATURE; OF LAW; OF NATURAL LAW; OF POSITIVE, PRIVATE, PUBLIC, NATIONAL, INTERNATIONAL, CIVIL, AND ECCLESIASTICAL LAW -- OF LEGAL JUSTICE AND OF PARTICULAR -- OF THE SINS OPPOSED THERETO (A)

(A)  
After the virtue of prudence, is the virtue of justice the most important of the other virtues?

Yes, after the virtue of prudence, which occupies a place apart in the order of the moral virtues and without which no one single virtue can exist, the most important among the other virtues is the virtue of justice (LVII.-CXXI.).
 
What is the virtue of justice?

It is that virtue which has for its object right or the just (LVII. 1).
 
What is meant by this?

By this is meant that the object of justice is to make respected among men those relations which are founded upon the respect due to existence and possession, which are legitimately the privilege of every human being (LVII. 1).
 
But how does one know that the existence or the possession of any one particular person is legitimately of such a nature or should be of such a nature?

One knows this by what natural reason tells concerning each man; also by that which, by common consent, is determined by the reason of different men; and also by the reason of those who are in authority whose office it is to regulate such matters (LVII. 2-4).
 
What is that law called which is founded upon what the natural reason dictates?

It is called the natural law (LVII. 2).
 
And that law which is determined by the common accord of different men, or that which is determined by those in authority whose duty it is to make regulations concerning the relations between men?

It is called positive law, which is divided into private law and public law; the latter is further divided into national and international according as there is question of private conventions or of the laws of a country, or of the laws agreed upon and established between different nations (LVII. 2).
 
What is the civil law and ecclesiastical law?

Civil law treats of the relations between men in so far as they are determined by the civil authority; ecclesiastical law in so far as they are determined by the ecclesiastical authority.


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