The essay below by Ryan T. Anderson on The Witherspoon Institute website is an excellent piece on the natural law. Edmund Burke outlined similar ideas about the duties inherent in man’s nature. See Edmund Burke on what it means to be a people.
Since I have just said a few words on natural law and economic freedom, I want to say a few words about a natural law conception of social justice and how it can help us now. Some people think social justice is a twentieth century invention of left-leaning thinkers, but this starts the history of social justice midstream. To understand its true meaning, we must look farther back to its real historical origins.
The first known use of the phrase “social justice” was by a Jesuit Thomist, Luigi Taparelli, in his multivolume work published between 1840 and 1843 titled Saggio teoretico di dritto naturale appoggiato sul fatto (A Theoretical Treatise on Natural Law Resting on Fact). I want to emphasize two arguments that Taparelli highlighted by coining the new phrase “social justice”: first, that man is social by nature and belongs to many societies and, second, that man has natural duties to others in justice.