124. What the natural law is and how obvious it is
124. WHAT THE NATURAL LAW IS AND HOW OBVIOUS IT IS
How can modern intellectuals deny the existence of a natural moral law?
. . . [T]he precepts of the natural law are to the practical reason what the first principles of demonstration (like the law of non-contradiction) are to the speculative reason, because both are self-evident principles. Now a thing is said to be self-evident in two ways: first, in itself; secondly, in relation to us. Any proposition is said to be self-evident in itself if its predicate is contained in the notion of the subject; although to one who knows not the definition of the subject it happens that such a proposition is not self-evident. For instance, this proposition, Man is a rational being, is in its very nature self-evident, since whoever says man says a rational being; yet to one who knows not what a man is, this proposition is not self-evident. Hence it is that . . . certain axioms or propositions are universally self-evident to all; and such are those propositions whose terms are known to all, such as Every whole is greater than its part, and things equal to one and the same are equal to one another. But some propositions are self-evident only to the wise, who understand the meaning of the terms of such propositions; thus to one who understands that an angel is not a body, it is self-evident that an angel is not circumscriptively in a place; but this is not certain to the unlearned. . . .
Now as being is the first thing that falls under the apprehension simply, so good is the first thing that falls under the apprehension of the practical reason, which is directed to action; since every agent acts for an end under the aspect of good. Consequently the first principle in the practical reason is one founded on the notion of good, viz. that good is that which all things seek after. Hence this is the first precept of law, that good is to be done and pursued, and evil is to be avoided. All other precepts of the natural law are based upon this, so that whatever the practical reason apprehends as man’s good or evil belong to the natural law as something to be done or avoided. . . .
. . . [A]ll those things to which man has a natural inclination are naturally apprehended by reason as being good. . . .[I]n man there is first of all an inclination to good in accordance with the nature which he has in common with all substances, inasmuch as every substance seeks the preservation of its own being according to its nature, and by reason of this inclination whatever is a means of preserving human life and of warding off its obstacles belongs to the natural law. Secondly, there is in man an inclination to things that pertain in him more specially according to that nature which he has in common with other animals; and in virtue of this inclination those things are said to belong to the natural law which nature has taught to all animals, such as sexual intercourse, education of offspring, and so forth. Thirdly, there is in man an inclination to good according to the nature of his reason, which nature is proper to him; thus man has a natural inclination to know the truth about God, and to live in society; and in this respect whatever pertains to this inclination belongs to the natural law (I-II,94,2).
. . . [T]here belong to the natural law first certain most general principles that are known to all, and secondly certain secondary and more detailed principles which are, as it were, conclusions following closely from first principles. As to these general principles, the natural law in the abstract can nowise be blotted out from men’s hearts. But it is blotted out in the case of a particular action in so far as reason is hindered from applying the general principle to a particular point of practice on account of concupiscence or some other passion . . . But as to the other, i.e., the secondary precepts, the natural law can be blotted out from the human heart either by evil persuasions, just as in speculative matters errors occur in respect of necessary conclusions, or by vicious customs and corrupt habits, as among some men theft and even unnatural vices, as the Apostle states (Rom 1) were not esteemed sinful (I-II,94,6).
Of course such extreme foolishness could never be found in our “Christian” civilization! Or are we so “educated” that we can no longer even comprehend St. Thomas’ ultra-simple argument above?