For some time people have asked me to comment on the relationship between the concept of natural law (and the related one of natural rights) and Stoicism. Part of the reason is that I profess to be a Stoic, and yet I reject the idea of natural law, which if didn’t exactly originate with the Stoics, was certainly greatly elaborated put on the map by them. What gives? The final prompt to sit down and write this was actually a recent, shall we say forceful exchange that I have had with Skeptic’s editor Michael Shermer, who is an advocate of natural rights. (The article that started our discussion was published in Scientific American; here is my first response; this is Michael’s response to me; and this is my response to his response.) This post will not cover the full history and philosophical debates on natural law (a comprehensive article can be found here), but will rather focus on the early versions of the concept, and especially on Stoicism — ancient and modern.

Ius naturale, or lex naturalis, asserts that certain rights are inherent by virtue of human nature, endowed by God or other transcendent source, but understandable by way of human reason. In a sense, then, moral natural law is something like scientific laws: in traditional views, up to Newton included, laws of nature in the scientific sense were thought of as being given by a Creator God (that is why they were referred to as “laws”), but human beings are smart enough to grasp them. My critical argument later in this post hinges on two propositions: I reject the notion of transcendent sources, and I don’t think natural moral laws — whatever they may be — are anything like laws of nature in the scientific sense.

Alfred Whitehead famously said that much of Western philosophy can be understood as a series of footnotes to Plato. Sure enough, people have attempted to pin the origin of the concept of natural law on Plato. The major sources are the Symposium and the Republic, especially the latter, in which Plato develops his idea of the Forms, and particularly the Form of the Good. This has (somehow) mind-independent existence, and yet can be grasped by human beings (especially philosophers, when they manage to get out of the mythical cave). The ideal Republic, says Plato, is “a city which would be established in accordance with nature.” (428e9) Still, Plato certainly did not have an explicit theory of natural law, and uses the term only rarely (in Gorgias 484 and Timaeus 83e).

The next, more convincing, candidate, is Aristotle. He does talk about natural rights in the Nicomachean Ethics (book V), but a lot of what is attributed to Aristotle in this case is the result of a conflation between natural law and natural rights by Thomas Aquinas, who also influenced (not for the better) the early medieval translations of Aristotle, once his works were recovered through the influence of the Muslim world. Still, Aristotle does explicitly talk about natural law in his Rhetoric, where he distinguishes between a “particular” law that varies from country to country and a “common” law that is in accordance to nature. However, some scholars suggest that Aristotle treated natural law as a potential strategy in rhetorical discourse, not as a thick metaphysical concept.

Which brings us to the Stoics and to Cicero, who really put the concept on the map. The ancient Stoics, as is well known, were pantheists. They thought that the universe is a living organism, which they called god. We are literally bits and pieces of the divine, and very special bits and pieces at that, since we participate in the highest version of the all-pervading pneuma (breath), the Logos, the ability to think rationally. For the Stoics, then, natural law simply meant the workings of the cosmos, which we are capable of apprehending via our sharing in the Logos. To live according to nature, for them, meant to live following an understanding of human nature, and human nature is the nature of a social being capable of reason.

“And this is why the end may be defined as life in accordance with nature, or, in other words, in accordance with our own human nature as well as that of the universe, a life in which we refrain from every action forbidden by the law common to all things, that is to say, the right reason which pervades all things. … Diogenes [of Babylon] then expressly declares the end to be to act with good reason in the selection of what is natural. Archedemus says the end is to live in the performance of all befitting actions.” (Diogenes Laertius, Lives and Opinions of the Eminent Philosophers, VII.85-88)

As I’ve pointed out in the past, this is not a simple appeal to nature, which would be a logical fallacy. The Stoics were too damn good logicians to fall for that! They did argue that whatever is natural is good, as it manifestly isn’t (anger, for instance, is natural, but the Stoics famously thought of it as a destructive emotion, to be avoided). Rather, the thought is more sophisticated: it begins with certain observations about the nature of the world and of humanity, and works its way, by philosophical reasoning, to what it means to act in a way that is consonant with both.

English historian A.J. Carlyle highlighted one of the major consequences of Stoic thought about natural law:

“There is no change in political theory so startling in its completeness as the change from the theory of Aristotle to the later philosophical view represented by Cicero and Seneca. … We think that this cannot be better exemplified than with regard to the theory of the equality of human nature.” (A History of Medieval Political Theory in the West, vol. 1. Edinburgh. pp. 8–9, 1903)

For his part, Charles H. McIlwain observes:

“The idea of the equality of men is the most profound contribution of the Stoics to political thought … its greatest influence is in the changed conception of law that in part resulted from it.” (The Growth of Political Thought in the West: From the Greeks to the End of the Middle Ages. New York. pp. 114–15, 1932)

Cicero also thought that natural law obliges us to work for the betterment of humankind. In De Legibus he argued that both justice and law originate in nature, and that it is the human mind that can grasp what nature tells us and act accordingly. In De Republica he writes:

“There is indeed a law, right reason, which is in accordance with nature; existing in all, unchangeable, eternal. Commanding us to do what is right, forbidding us to do what is wrong. It has dominion over good men, but possesses no influence over bad ones. No other law can be substituted for it, no part of it can be taken away, nor can it be abrogated altogether. Neither the people or the senate can absolve from it. It is not one thing at Rome, and another thing at Athens: one thing to-day, and another thing to-morrow; but it is eternal and immutable for all nations and for all time.” (V.29-30)

And here is where I’m going to disagree. First off, if we want to draw an analogy between moral and scientific natural laws we immediately get into trouble, because of what Cicero writes here: “It has dominion over good men, but possesses no influence over bad ones.” That certainly goes for moral law, but not for scientific ones. You may disagree with the law of gravity, say, but you will nonetheless going to comply with it. This is an important disanalogy, because it hints at the idea that the word “law” is used in multiple ways, and that one should think of natural moral laws as more akin to what is called positive law (i.e., the kind of laws we come up with to regulate actual societal interactions) than to something unavoidable (or inalienable) like scientific laws.

Second, and more important, I am not a pantheist, so I don’t think that the universe is an organism with its own aims, an organism whose intentions need to be read by human mind so that we can act accordingly. The universe just is, and it is indifferent to us, it provides neither guidance nor hindrance, from a moral perspective.

But if that is the case, why do I still call myself a Stoic? What happened to “live according to nature”? I still think the Stoics got enough right to feel comfortable within their philosophy. What they got right is the idea that morality is about improving social living, that human beings are quintessentially social animals (we do not flourish, and in fact barely survive, in isolation), and that we are indeed equipped with the ability to reason about things. So it is still perfectly coherent to say that living according to nature means to apply reason to social living, just as Marcus says:

“Do you have reason? I have. Why then do you not use it? … Do what is necessary, and whatever the reason of a social animal naturally requires, and as it requires.” (Meditations IV.13 and IV.24)

The problem is that reason and facts about human nature are not in a simple, one-to-one correspondence. You can’t read what you ought to do straight from what is. You can, however, bridge the so-called is/ought gap, by using facts about human nature as empirical axioms, and then deploying a particular philosophical framework, such as Stoicism, to arrive at guidance for ethical action. The upshot is that you can still do Stoic philosophy. The catch is that there is more than one way to translate facts about human nature into philosophical moral precepts (in philosophy this phenomenon is called under-determination). Which means that if Stoicism doesn’t do it for you, you can try Buddhism, or Christianity. Heck, even Epicureanism might do it! From this perspective, it makes no sense to ask whether Stoicism is “true” (that’s a category mistake). But it makes sense to say that it is beautiful, coherent, and useful.