THERE IS SOME INCONSISTENCY in John Calvin's theological anthropology of "total depravity" and his express acceptance of the existence of a natural moral law. This inconsistency has led to varied interpretations of his thought. At one extreme perhaps is Karl Barth, who grudgingly admitted that Calvin mouthed natural law concepts, but believed that the consistent application of Calvin's doctrines of total depravity necessarily required rejection of the existence of a natural moral law. At the other extreme, one may find the Calvin scholar, John T. McNeil, who maintained that there was no essential discontinuity between Calvin's view of natural law and its medieval predecessors, making Calvin almost a crypto-Thomist.
It is a fact that Calvin's opinion of fallen man is brutally pessimistic: "such is the depravity of his nature," Calvin insists, "that he cannot move and act except in the direction of evil" (qua tamen est naturae pravitate, nisi ad malum moveri et agi). Institutes, II.3.5. A nature that cannot move and act except in the direction of evil cannot yield forth fruit that is, even in a manner, virtuous and good, much less a source of law and a latent voice of God. Yet it is indisputable, if not entirely consistent with his total depravity theory, that Calvin expressly maintained a notion of natural law, using the term lex naturalis often enough. It is found in various places in his magnum opus, the Institutes of Christian Religion, even in language traditional. "God provided man's soul with a mind, by which to distinguish good from evil, right from wrong; and, with the light of reason as guide, to distinguish what should be followed from what should be avoided." Institutes, I.15.8; see also II.2.12, 22, 24; II.8.1; IV.20.16. It is also mentioned in his Commentary on the Book of Psalms (discussing Psalm 119:52) and his Commentary on Romans (discussing Romans 2:15).
This is hardly the place to develop a full and comprehensive review of Calvin's doctrine of natural law. The literature in this area is immense, variform, and inconsistent. Any full treatment would probably be problematic anyway, since Calvin never developed any systematic treatment of the natural law. (Stephen J. Grabill, Rediscovering The Natural Law in Reformed Theological Ethics (Grand Rapids: Eerdmans, 2006), 91). It appears, further, that Calvin may have adopted notions of the natural law from the intellectual milieu almost unthinkingly or unguardedly, and without fully integrating them into the fundamentals of his theological doctrine. (See R.S. Clark, Calvin on the Lex Naturalis, Stulos Theological Journal 6:1-2 (May-Nov 1998), 3.) So knowledge of what Calvin exactly thought about the natural law is probably foreclosed to us, at least with any certainty. Overarchingly, it may be said, however, that Calvin's negative assessment of man's post-lapsarian epistemic and moral abilities resulted in a severe restriction of the role and effect of the natural law in his doctrine.
Some things appear to be clear regarding Calvin's assessment of the natural law. The first is that Calvin's view of the natural law is markedly more negative that St. Thomas's view, and its role much more limited and circumscribed than the role St. Thomas gives it. Related to this view is a second feature of Calvin's doctrine of the natural law: that being that Calvin seems to have given short shrift to the role of practical reason in the natural law, emphasizing almost exclusively the role of the natural law in conscience. The third feature seems that Calvin appeared to have identified the natural law with the Ten Commandments or Decalogue and so he neglected any reason-based or philosophical basis for determining its content. The fourth feature is that Calvin, consistent with many reformers, including Luther who influenced him, nowhere links the natural law with the eternal law of God. The severance of any linkage between the natural law and the eternal law, and the collapse of the distinction between them, is probably a result of Calvin's rejection of a realistic philosophy and an adoption of a nominalistic one. There is therefore significant discontinuity between Calvin's notion of the natural law and the received teaching, perhaps most systematically framed by St. Thomas Aquinas.
Title Page to Calvin's Institute of Christian Religion