Part of our resistance to the idea of natural law (besides the objection that the use of the term ‘natural law’ seems to belong exclusively to the Roman Catholic Church), is the multiple ambiguity of the adjective ‘natural’. Suppose an apple tree; the apples that it bears are natural, they are the product of the processes that are intrinsic to an apple tree’s being an apple tree and not a cherry tree. If someone attaches wax apples to the apple tree, then these are not natural apples, for they are not true apples. But now suppose that the apple tree is diseased and what is produces are scabby, gnarled specimens of applehood, hardly edible. These are natural in the sense that they are the true product of the tree, but they are not natural in another sense. It’s not natural for an apple tree to produce gnarled and inedible fruit. The fruit have been contaminated by disease of some kind, and so they are not natural in the (further) sense in which honey without any additives is ‘natural honey’, that is pure, uncontaminated honey. So there’s ‘natural’ in the sense of being natural as opposed to artificial, or conventional, or ‘introduced’, and natural in the sense of true and pure as against contaminated or added to. Two other senses of ‘natural’ are relevant here: natural in the sense of universal, and natural in the sense of original – It’s natural for the sun to rise, because the sun rises every day, or for apple trees to bear apples; it is natural, in the sense of original, for a viper to bite.
What of natural law? How is ‘natural’ being used here? In the thought of people such as Calvin and Aquinas, law is natural in the sense of being both universal and original; the presence of such law, and its recognition as such by men and women, are part of mankind’s primitive endowment. But it’s not natural in the sense that its operation in human life is normal or pure, rather it is presently diseased and contaminated by the disease and contamination of fallen nature. In the case of the operation of the natural law, the Fall has intervened.
Unless we are prepared to say that the Fall dehumanised the human race, turning us all into brute beasts, it is clear that some such distinction between nature and supernature is logically required by the Fall. For the Fall does not literally de-humanise, depriving mankind of its essential nature, for then human beings would become other than human. While it is true that occasionally Scripture refers to fallen human nature as 'bestial', in such places the reference is to the moral practices of fallen men and women, and not to their humanity that, despite the Fall, retains its essential characteristics. For essential features, such as reason and conscience and will, remain after the Fall, as (I believe) Paul implies in Romans 2, though these are corrupted and depraved by it. The supernatural gifts - principally holiness and true righteousness - were from a logical and metaphysical point of view 'contingent', but nevertheless they were vital from the point of view of mankind's health and prospects.
As a result of the Fall mankind’s supernatural gifts comprising the imago dei are vitiated. To be shorn of supernatural gifts is to have the ordering of the various natural powers and abilities that remain removed. The consequence is 'total depravity', where the adjective is understood in an extensive rather than an intensive sense. Writing of fallen mankind Calvin says
True! he has a mind capable of understanding, though incapable of attaining to heavenly and spiritual wisdom; he has some discernment of what is honourable; he has some sense of the divinity, though he cannot reach the true knowledge of God. But to what does these amount? They certainly do not refute the doctrine of Augustine – a doctrine confirmed by the common suffrages even of the Schoolmen, that after the fall, the free gifts on which salvation depends were withdrawn, and the natural gifts corrupted and defiled.
So - to use a set of modern distinctions – the biblical view of natural law is not that the 'natural' as it was created is equivalent to the 'secular', a set of powers that are at best neutral as between the claims of theism and atheism, or between rival religions and no religion at all, say. The Fall does not mean that the contrast between ‘natural’ and ‘supernatural’ is obliterated, but that (in the sense in which we re using it) the ‘natural’ is equivalent to the God-given. So that natural law has a supernatural origin, but it is not miraculous but it is universal, innate etc. in the senses that have been set out.
However, as a consequence of this, ‘natural’ also testifies to the fact that man's nature is intrinsically religious, intrinsically orientated to the knowledge of God, which was ordered in unfallen mankind, but became perverted (not extinguished) in fallen mankind. What Calvin calls the sensus divinitatis is part of the essence of human nature, as is shown by the fact that it remains, albeit in a perverted form, after the Fall. An apple tree produces apple leaves even though its blossom and fruit-producing powers have been extinguished by the blight. And similarly with the other aspects of mankind’s original powers. The 'ordering' is not therefore a religious icing on a secular cake, it is the ordering of a nature which is, for Calvin, essentially religious.
What is true of Calvin is true, surprisingly perhaps, of Thomas Aquinas.
There is a three-fold good in original, unfallen human nature; first, the constitutive principles of nature, body and soul, and the physical and mental properties that they express; and second, there are the powers of body and soul which (in a state unimpaired by sin) incline humankind to virtue. Finally there is the 'gift of original justice', natural in the sense that it was originally universal, bestowed in Adam on all mankind, but not entailed by nature.
Aquinas claims that of the three, the first is neither destroyed nor diminished by sin, the second is lessened through sin, and the third is totally removed. Let us look further at what chiefly interests us here, the first two.
In saying that sin does not destroy or diminish the constitutive principles or powers of the soul (nec tollitur ned diminuitur) Aquinas claims that human nature remains intact, not one of its essential features or powers is lost. The first man was every bit a man even when fallen and sinful as he was before; he remains a body-soul composite, he retains his humanity with its natural and mental powers, and so on. The Fall did not denature. Further, the pursuit of virtue with which humankind was originally endowed, prior to the Fall, which is also essential to human nature, is not removed but according to Thomas it is 'weakened'. So 'while nature itself is not intrinsically changed through a deviation in voluntary action, still its inclination is changed with regard to direction towards a term'. Sin lessens the good of nature in that it is 'a diminution of this good inasmuch as it involves the disorder of an act' So we may say that human nature, though intact, is disordered by sin. It is essential to man that he acts in accordance with reason, purposively, and that he seeks the good, (even though he may have a wrong view of what the good is), and so these features cannot be taken away without denaturing him. What happens is that the inclination to the good is lessened, in that it is hindered, and is wounded, receiving the wounds of weakness, ignorance, malice and concupiscence. Other goods are substituted for the true good.
So according to Aquinas, as a result of the Fall a human being remains as such, but his nature, that which is constitutive of him as a human being is weakened or impaired in its ‘connatural inclination to virtue’ by the total loss of what Aquinas calls ‘the gift of original justice’.
In his book Aquinas, Calvin, and Contemporary Protestant Thought , Arvin Vos stresses this point against modern Reformed interpreters of Thomas. He also points out that according to Aquinas the moral virtues, which we all may possess by nature, are not possible to be addressed to God without the theological virtue of charity. As Thomas puts it
Only the infused virtues are perfect , and deserve to be called virtues absolutely, since they direct a man well to the absolutely ultimate end. The other virtues, those namely that are acquired, are virtues in a limited sense, not without qualification. They direct a man well in respect to what i final in some particular field, not in the whole of life. Accordingly, on the text, All that is not of faith is sin, the Gloss comments from Augustine, He that fails to acknowledge the truth has no virtue, even if his conduct be good.
So how do the Dutch Calvinists come to emphasise common grace at the expense of natural law? What is the explanation of Bavinck's mistake? It is, I believe, that he was working with a Counter-Reformation view of nature and grace, a view ultimately derived from Cajetan, and reading it back into Calvin's own situation: a classic case of anachronism. Whether or not this is the precise explanation, it is fairly clear that Bavinck's understanding of the Roman Catholic view of the distinction between nature and grace draws that distinction in much sharper lines than it is found historically in Augustine and Aquinas. Indeed, it is another account altogether.
So the idea here is that nature and grace entail two sets of powers or virtues, and these sets are contingently connected in that the set of powers which comprise 'grace' can come apart from the set of powers that comprise 'nature'. In addition there is a basicness to nature in that while the gracious set of powers can come apart from nature, and nature thus exist on its own, the opposite cannot happen. Grace cannot exist apart from nature, though nature can exist without grace..
Bavinck says that the way in which common grace works is in traces of the image of God continuing in those who are fallen and who are not enjoying saving grace. For example, understanding and reason remain, as do the possession of natural gifts in certain individuals. Calvin would not demur. But his explanation is not that reason and understanding are part of the image of God, but that reason and understanding remain, though these are not part of the image, though they are necessary conditions of possessing the image, and are nevertheless damaged as a result of the Fall.
To say that a human ability or activity is the effect of common grace or that it is the working of nature, human nature, are thus two ways of saying the same thing, or almost the same thing. What the phrase ’common grace’ brings out is that these abilities and activities, as found in fallen and unregenerate human nature, are the result of undeserved, divine goodness. The effects of the Fall on human nature could have been worse than they are, and why they are not worse than they are is due to God’s undeserved goodness. ‘Nature’ looks at the same phenomenon from another angle, focusing on the persisting structures of human nature. How are the gifts of common grace expressed? In the workings of human nature, created in the image of God and now fallen and suffering loss and perversion as a consequence. Due to divine goodness, the Fall has resulted in loss and perversion but not in obliteration. So I argue that these expressions ;’common grace’ and ‘nature’ are complementary descriptions of the same phenomenon; they are not at odds with each other, and so they are not to be set in opposition to each other.