Source: Mirror of Justice.
“…Moral intuition is also a kind of experience, different from sense perception – and neither of them infallible.
Our belief in natural law is not impaired by the fact that the results of this intuition are not necessarily identical in everyone’s mind, always and everywhere, nor by the fact that centuries were needed before people recognized the good and evil of their various actions and institutions – before they admitted, for example, that torture is evil and equality before the law good. This has also been the case with many discoveries in empirical science: it took centuries before people realized that their ordinary intuitions were wrong: that the sun does not revolve around the earth, or that a force is not necessary to cause movement, or that events are never absolutely simultaneous. All these erroneous beliefs were natural and understandable. So why should we not accept that the principles and norms of natural law reveal themselves to us
gradually: that we must go through a process of growth before we understand certain moral truths and laws and recognize them as such? (Although it should be said that since antiquity there have been people who preached those principles and norms with full conviction – without, however, gaining universal approval.)
There is no reason to accept the nihilistic doctrine that because various contradictory norms have been accepted and applied at various times and in various places, they are all, in terms of Reason, equally justified, which is to say equally groundless. While belief in natural law does not – I repeat – require belief in the existence of God as a necessary premise, it does require the belief in something that one might call the moral (in addition to the physical) constitution of Being – a constitution that converges with the rule of Reason in the universe.
All the evils of the human world, its endless stupidity and suffering, cannot
impair our belief in natural law in this sense. Two other realms of
intuition – perception and mathematics – also require suppositions that cannot be proved but are indispensable for the knowledge we acquire by these intuitions. Our life as rational creatures occurs in a realm that is
constructed with the aid of various non-empirical but fundamental courts of
appeal, among them truth and goodness. Nor need our belief in natural law
be impaired by the fact that it is not universally observed. This fact
was well known to Seneca and Cicero, to Gratian and Suarez, to Grotius and
Kant, but it did not weaken their conviction that the rules of natural law are
valid, no matter how often they are violated.