What is, for Kant, a Law of Nature?

Eric Watkins

Univ. of California, San Diego

Abstract: 
The concept of a law of nature plays a number of highly visible roles in Kant’s theoretical philosophy. Yet we can fully appreciate these roles only if we have an accurate understanding of what his conception of a law of nature is. Investigating the broader historical and philosophical tradition out of which Kant’s conception of a law of nature emerged provides crucial insights. For this tradition contains two uses of the term “law” that, when taken together, present a challenge to the very idea of a law of nature that one can see Kant responding to in a novel way. The one use of the term derives from the so-called natural law tradition, which argues that obligation arises only on the basis of natural law, where a natural law can be established only through the act of a (superior) lawgiver who governs (inferior) subjects by placing them under an obligation to perform certain actions. It is also often added that natural law can apply only to beings endowed with reason and free will, since only such beings can understand the obligation that the law places them under and then decide whether or not to obey the law. The other use of the term “law” derives from the conception and practice of natural science in the early modern period and presupposes that natural science consists in the search for a small number of mathematically precise laws of nature. Taking these uses together reveals an important challenge to the very idea of a law of nature: How is it possible for a law to govern the inanimate objects found in nature? If no legislator enacts such a law and if many of the objects in nature are not rational beings and cannot therefore be obligated to act as the law demands, how can there be such a thing as a law of nature? Though several responses are possible, I maintain that Kant’s answer depends on a concept of law that has a genuinely univocal meaning at its core, but one that can be instantiated in different ways in the theoretical and practical contexts of laws of nature and the moral law. Specifically, the core meaning of law that is univocal between laws of nature and the moral law contains two elements. First, the concept of law requires an objective or necessary rule. Second, a law can be valid only if a proper authority has prescribed it to a particular domain through an appropriate act. This core meaning of law is then instantiated in different ways in the different cases of laws of nature and the moral law. While Kant insists on every kind of law being the result of a spontaneous and active faculty that is endowed with the authority to legislate, the notion of necessity takes on different forms, since the laws of nature are responsible for determination, while the moral law can give rise to obligation. In light of these differences, Kant can then respond to the challenge raised above by noting that the requirement that the subjects governed by law must be rational (and free) obtains for the case of obligation, not for all cases of determination, despite the fact that both involve a necessary rule and allow for an appropriate sense in which the law can be said to govern subjects.