Natural law has an important place in Catholic tradition. Nonetheless, as with much of Catholic tradition, it has often been misunderstood and even abused. Many who have suggested that we abandon the notion of natural law have done so mostly because of such misunderstandings — what they want to dismiss often is something which should be rejected. What is needed is an understanding of what natural law is, its applicability, and its limits. What is offered here can only serve as a brief outline of these concerns.
Natural law is founded upon the idea that what God created is good, and that if what God created follows its nature, because its nature is good, it will be good. Each part of creation has its own essence, and its proper place in the order of being. For those who are alive and therefore, have some sort of self-movement, this place is not limited; rather, it is meant to be open-ended. Not only does their potential determine a possible range of activity, there is also the possibility of God’s grace giving them an even greater range of potentiality than they would have of themselves.
This leads us to the first way people misunderstand natural law: when discussing what a thing is and its potentiality, they ignore the relationship between grace and nature, and assume nature is some sort of closed-in-itself entity. But that error closes off creation from God — and therefore what is natural could not be said to be good for God is the source and end of every good. In this way, their view of natural law could never lead to what is good, and this explains why rigid legalistic notions of natural law, which seek to define things in a static way, end up far from good in execution, because it cuts out grace from the order of activity.
But this leads us to the second, and perhaps, more difficult problem. The world as it was created was closed off to grace by the power of sin. While the nature of everything remains good, their potentiality is less than their nature, because of their fallen mode of existence. We see a world cut up in struggle with itself. Whether or not one wants to explain the corruption of nature as being at the hands of humanity alone, or if one thinks it is a shared fall, in either case, the world is fallen, and what appears to us in nature is not what is natural, but what is sub-natural. Defining what is good based upon this fallen, graceless way of life can only end up in disaster. In describing the possible errors one can have with nature, John Burkman describes this error as the divinization of nature:
The second error – the divinization of nature —is typical of theologies which idealize old-growth forests or other untouched nature. Such theologies usually wind up affirming the ‘naturalness’ of predation and parasitism in nature. For if ‘untouched’ or ‘pristine’ nature is what we consider to be the ideal, then we would seem to have to affirm the continuous cycles of predation, death, and decay as necessary and good.
In other words, in the fallen world, what should be natural and good is corrupted. We cannot rely upon the world as it is for our moral theology, otherwise we would find justification for all kinds of evils, because such evils exist all around us. This points out the difficulty which exists when trying to posit natural law: we posit it according to what we see in the world around us. What we see, however, isn’t natural. We have to extrapolate from the sub-natural mode of existence. Mistakes can, and do happen. The brutality of the fallen world is the brutality of sin, the brutality of death. The law of the jungle is the necessity of sin. We should understand it, and even understand how humanity itself remains affected by this law because of its sin, but we should also understand how we are not limited to it, and that our foundation for morality cannot be based upon it (for if we did, we would call that which is corrupt, good).
When we discuss natural law, perhaps the greatest problem lies in the fact that it is an intellectual exercise trying to discern what one is to do — in other words, we try to establish natural law for the sake of deliberation. But nature does not need to deliberate in order to act — the will, in its pure form, acts according to its good desires; but because of the fall, our mode of willing is unnatural, and we desire what we should not. Therefore, we must deliberative to discern if our desire is right or wrong. In other words, even discussing morality and ethical standards shows we are interacting with a sub-natural realm of discourse. And this shows it is something less than the good, even before it becomes rigid and closed in on itself (becoming even further from the good). Natural law discussion by this fact must not be confused with the natural law itself. If it were really natural, we would not have to discern what is contained in it, but would know it without such discernment. Indeed, if our mode of willing were natural, we would will what is good without having any moral question as to what we should do; we would just act and it would be good.
 John Burkman, “Is the Consistent Ethic of Life Consistent without a Concern for Animals?” Animals on the Agenda. Ed. Andrew Linzey and Dorothy Yomamoto (London: SCM Press Ltd., 1998), 241.
 St Maximus the Confessor makes this point quite well in his debate with Patriarch Pyrrhus. See The Disputation with Pyrrhus Of Our Father Among the Saints Maximus the Confessor. Trans. Joseph P. Farrell (Yonkers, NY: St Tikhon’s Seminary Press, 1990).