Definition of Natural Law from the Position of the Catholic Church
According to the Catholic Church, Natural law is inherent in all humans. Saint Thomas Aquinas tells that “God is the source of Natural law” and Natural law is that part of the eternal law governing human conduct accessible through human reason.” In other words, Natural law is more than a divine medium to rule man. It is something that pertains to the divine gift of human reason.
Moreover, Natural Law “hinges upon the desire for God and submission to Him, as well as upon the sense that the other is one’s equal,” (CCC 1955). Natural Law also expresses the dignity of the person and determines the basis for his fundamental rights and duties (CCC 1956, 1978). The first principle of Natural Law is “good is to be done and pursued, and evil avoided,” (I.II, Q. 94; CCC 1954). All other precepts of Natural Law rest upon this. William Blackstone once mentioned: “This law of nature, being co-eval with mankind and dictated by God himself, is, of course, superior in obligation to any other. It is binding over all the globe, in all countries, and at all times: no human laws are of any validity, if contrary to this, and much of them as are valid to derive all their force, and all their authority, mediately or immediately, from this original.” Indeed Natural law is timeless — “it is immutable and permanent … the rules that express it remain substantially valid.” (CCC 1958).
 Thomas Aquinas, Summa Theologiae (Dominican Fathers trans, Ave Maria, 1948) I-II, q 94. [PDF]
 Thomas Aquinas, q 93.
 Thomas Aquinas, q 94.
 Jan Garrett, “Aquinas on Law,”https://people.wku.edu/jan.garrett/302/aquinlaw.htm (assessed on May 25, 2021).
 Jan Garrett, “Aquinas on Law.”