Passion or evil habits or an evil disposition,(see next posts on temperaments and predominant faults), can corrupt or block natural law.
Consequently we must say that the natural law, as to general principles, is the same for all, both as to rectitude and as to knowledge. But as to certain matters of detail, which are conclusions, as it were, of those general principles, it is the same for all in the majority of cases, both as to rectitude and as to knowledge; and yet in some few cases it may fail, both as to rectitude, by reason of certain obstacles (just as natures subject to generation and corruption fail in some few cases on account of some obstacle), and as to knowledge, since in some the reason is perverted by passion, or evil habit, or an evil disposition of nature; thus formerly, theft, although it is expressly contrary to the natural law, was not considered wrong among the Germans, as Julius Caesar relates (De Bello Gall. vi).
Reply to Objection 1. The meaning of the sentence quoted is not that whatever is contained in the Law and the Gospel belongs to the natural law, since they contain many things that are above nature; but that whatever belongs to the natural law is fully contained in them. Wherefore Gratian, after saying that "the natural law is what is contained in the Law and the Gospel," adds at once, by way of example, "by which everyone is commanded to do to others as he would be done by."
Reply to Objection 2. The saying of the Philosopher is to be understood of things that are naturally just, not as general principles, but as conclusions drawn from them, having rectitude in the majority of cases, but failing in a few.
Reply to Objection 3. As, in man, reason rules and commands the other powers, so all the natural inclinations belonging to the other powers must needs be directed according to reason. Wherefore it is universally right for all men, that all their inclinations should be directed according to reason.
To summarize so far: all men by the fact that they are human have natural law as part of their being.
All men are given reason, the rational ability to be human, to chose God and to chose grace.
No one is not given grace.
All inclinations come from reason. If reason is following its true end, that is God, men will choose God
Supernatural law, such as the Beatitudes, is based on natural law and informed by grace.
The Church dispenses grace through the sacraments.
But, what if one meets people who not only deny natural law, or do not think of it, but are living against reason?
to be continued...