From Cicero to Aquinas to Jefferson, the Long Road of Natural Law

There is a sentence that every tyrant in history has wanted to say and every free people has refused to accept: "It was legal." The decree was signed. The vote was taken. The forms were followed. So what is your complaint?

The complaint is older than the tyrant, older than the decree, older than the nation that issued it. It is the conviction that there is a law above the law, a moral order that binds kings and parliaments and majorities, and that ordinary people can know it by reason. That conviction has a name, natural law, and it has a history that runs for more than two thousand years without a break, from a Greek tragedy to a Roman senator to an Italian friar to an English clergyman to a Virginia planter to a Baptist minister writing in the margins of a newspaper in an Alabama jail cell. Here it is, in order.

Before the philosophers: Antigone

The story begins on the stage. In Sophocles' Antigone, first performed in Athens around 441 BC, the king Creon forbids anyone to bury the body of a rebel. Antigone, the rebel's sister, buries him anyway. When Creon demands to know how she dared break his law, she answers that his edict could not override the unwritten and unfailing laws of the gods, which are not of today or yesterday but live forever, and no one knows when they first appeared.

That is the whole idea in seed: a ruler's decree is not the final word, because there is a law no ruler wrote. Aristotle later cited Antigone's speech by name in his Rhetoric as an example of appeal to a law that is universal and according to nature.

Aristotle and natural justice

Aristotle, who taught in Athens in the fourth century BC, gave the idea its first philosophical form. In Book V of the Nicomachean Ethics, he divides political justice into two parts. One part is natural, and has the same force everywhere and does not depend on people's thinking this or that. The other part is legal or conventional, things that were originally indifferent but became binding once laid down, like the amount of a fee or the form of a sacrifice. His illustration is memorable: fire burns both here and in Persia.

Notice the distinction, because the whole later tradition depends on it. Much of law really is convention: which side of the road to drive on, how many days to file an appeal. But some of it is not. That murder is wrong is not a local custom that happens to prevail in Athens. It is true in Persia too.

Aristotle's account had a dark corner, and honesty requires naming it. In the Politics, he argued that some people are slaves by nature. We will come back to that, because the natural law tradition itself would eventually supply the answer.

The Stoics and Cicero: true law is right reason

The Stoic philosophers, beginning with Zeno of Citium around 300 BC, taught that the universe is ordered by reason and that every human being shares in that reason. From that followed a radical idea for the ancient world: all men are citizens of one cosmos, under one law.

The man who carried the idea to Rome, and through Rome to the West, was Marcus Tullius Cicero (106 to 43 BC), lawyer, consul, orator, and finally a victim of the very tyranny he warned against, murdered on the order of Mark Antony after the death of the republic. In Book III of De Re Publica, written in the 50s BC, Cicero put natural law into words that every later writer would echo. The passage survives because the Christian writer Lactantius quoted it. In a standard English translation:

True law is right reason in agreement with nature; it is of universal application, unchanging and everlasting.

Cicero goes on: we cannot be freed from its obligations by senate or people; there will not be different laws at Rome and at Athens, or different laws now and in the future, but one eternal and unchangeable law will be valid for all nations and all times. Whoever disobeys it, he says, is fleeing from himself and denying his human nature.

Read that last clause twice. For Cicero, the natural law is not an imposition from outside. It is the law of what we are. To violate it is to act against our own nature.

Paul, Augustine and the law written on the heart

Christianity received the idea and deepened it. Writing to the church in Rome around AD 57, the apostle Paul observed that Gentiles who did not have the law of Moses nevertheless knew right from wrong. In the King James rendering of Romans 2:14 and 15, they "do by nature the things contained in the law" and "shew the work of the law written in their hearts". The moral law, in other words, is not only in Scripture. It is in every human conscience.

Augustine of Hippo, writing in North Africa around AD 400, added the line that would echo for fifteen centuries. In his dialogue On Free Choice of the Will, he says that a law which is not just does not seem to be a law at all. The thought runs both ways: law has authority because it is just, and an unjust command lacks the authority it claims.

Aquinas puts it in order

The great systematizer was Thomas Aquinas (1225 to 1274), an Italian Dominican friar who taught in Paris and Naples. In the First Part of the Second Part of his Summa Theologiae, in the Treatise on Law that opens at question 90, he defined law itself as an ordinance of reason for the common good, made by him who has care of the community, and promulgated. Every word in that definition is a limit. An ordinance of reason, not of mere will. For the common good, not a faction's. Made by legitimate authority. Promulgated, so people can know it.

Then he distinguished four kinds of law:

1. Eternal law: God's reason governing all creation.
2. Natural law: the rational creature's participation in the eternal law, the part of it human beings can grasp by reason. Its first precept is that good is to be done and pursued, and evil avoided, and from it follow inclinations to preserve life, to raise children, to know the truth about God, and to live in society.
3. Human law: the particular rules communities make to apply the natural law to their circumstances, like setting penalties for theft.
4. Divine law: the law revealed in Scripture, which guides people toward their final end.

And then the critical move. Human law, Aquinas says, has the nature of law only insofar as it derives from the natural law. If it deviates from the natural law in some point, it is no longer law but a perversion of law. He quotes Augustine to make the point. An unjust law binds the conscience only to the degree that disobeying it would cause scandal or greater disorder, and a law commanding something against divine law must never be obeyed.

That was a revolutionary claim to make in a world of kings, and Aquinas made it calmly, in the measured question-and-answer form of a university lecture.

Hooker, Grotius and Locke

The idea survived the Reformation, which split Christendom but not the natural law tradition.

Richard Hooker (1554 to 1600), a clergyman of the Church of England, published the first books of Of the Laws of Ecclesiastical Polity in 1594. Hooker took Aquinas's framework into the English Protestant world: law flows from reason, and the authority of human laws depends on their agreement with the law of reason. John Locke would cite him repeatedly in the Second Treatise, calling him "the judicious Hooker".

Hugo Grotius (1583 to 1645), the Dutch jurist, published On the Law of War and Peace in 1625, during the Thirty Years' War. Grotius wanted a law that Catholics and Protestants, and even nations of no faith, could recognize, and he argued that the natural law would have some force even if, per impossibile, one granted that there is no God, a hypothetical he immediately called the greatest wickedness. His aim was not to remove God but to show that the moral law is rooted in the nature of things and can be known by any reasoning person. That made natural law the foundation of international law.

Then Locke (1632 to 1704). His Second Treatise, published at the end of 1689, opens its account of the state of nature in section 6 with the tradition in a single sentence:

The state of nature has a law of nature to govern it, which obliges every one: and reason, which is that law, teaches all mankind, who will but consult it, that being all equal and independent, no one ought to harm another in his life, health, liberty, or possessions.

Locke's contribution was to draw from the natural law a set of natural rights, held by each person before any government exists, which government is instituted to protect. How those rights become the basis of legitimate government is traced in Consent of the Governed Was a Precise Idea in Locke, Not a Slogan.

Blackstone, Hamilton and the Declaration

By the 1760s, the tradition had reached the American lawyer's bookshelf in its most accessible form. William Blackstone's Commentaries (1765 to 1769) declared that the law of nature, dictated by God himself, is superior in obligation to any other, and that no human laws are of any validity if contrary to it. The book's influence is profiled in Blackstone's Three Absolute Rights and Why Every Founder Owned His Book.

In 1775 a college student named Alexander Hamilton, answering a Loyalist pamphleteer in The Farmer Refuted, put the American version of the idea in a sentence:

The sacred rights of mankind are not to be rummaged for, among old parchments, or musty records. They are written, as with a sun beam, in the whole volume of human nature, by the hand of the divinity itself; and can never be erased or obscured by mortal power.

A year later the Continental Congress adopted a Declaration that opens by appealing to "the Laws of Nature and of Nature's God" and grounds the case for independence in self-evident truths: that all men are created equal, that they are endowed by their Creator with certain unalienable rights. Unalienable, because they come from a source no government controls, a point developed in Unalienable Means You Cannot Even Give Your Rights Away, and Here Is Why.

Jefferson himself later told us where the ideas came from. In an 1825 letter to Henry Lee, he wrote that the Declaration was intended to be "an expression of the American mind", drawing its authority from the harmonizing sentiments of the day as expressed in conversation, letters, printed essays and the elementary books of public right, and he named them: Aristotle, Cicero, Locke and Sidney. There is the road, in the author's own words.

Birmingham, 1963

The tradition was not a museum piece once the Declaration was signed. Its most powerful modern statement came from a jail cell.

In April 1963 Martin Luther King Jr. was arrested in Birmingham, Alabama, for leading demonstrations in defiance of a court injunction. A group of eight white clergymen had published a statement calling the protests unwise and untimely. King's answer, dated April 16, 1963, is the Letter from Birmingham Jail. Asked how he could urge people to obey some laws, such as the Supreme Court's decision in Brown v. Board of Education (1954), and break others, he answered with the tradition:

One has not only a legal but a moral responsibility to obey just laws. Conversely, one has a moral responsibility to disobey unjust laws. I would agree with St. Augustine that "an unjust law is no law at all."

And then he defined the difference, naming his source:

To put it in the terms of St. Thomas Aquinas: An unjust law is a human law that is not rooted in eternal law and natural law.

King also insisted that anyone who breaks an unjust law must do so openly, lovingly, and with a willingness to accept the penalty. That is not anarchy. It is the highest respect for law, the Aquinas position that an unjust law lacks authority combined with a refusal to cause the disorder Aquinas warned against. The road from Cicero ran straight through Birmingham.

The strongest objection, and the answer

The strongest case against natural law comes from the school called legal positivism, and conservatives should take it seriously, because part of it sounds like us. Stated fairly: law and morality are different things. Law is what the legitimate authority has enacted, nothing more. Jeremy Bentham and later John Austin argued that rights exist only when a sovereign enforces them. Oliver Wendell Holmes Jr. said law is simply a prediction of what courts will do. Natural law, on this account, is dangerous for two reasons. It is vague, so everyone claims it for his side. And it invites judges to substitute their moral views for the written law, which is exactly what conservatives complain about when activist courts invent rights. Worse, the tradition's own founder, Aristotle, used "nature" to justify slavery.

Here is the answer in four parts.

1. Positivism has no answer to lawful tyranny. If law is only what the sovereign enacts, then the Nuremberg Laws of 1935 were law, the Fugitive Slave Act of 1850 was law, and Birmingham's segregation ordinances were law, and there is nothing to say against them except that one dislikes them. After 1945 the Allied tribunal at Nuremberg rejected the defense that following the orders and laws of one's own state excused crimes against humanity. That rejection rests on the very idea that some wrongs no statute can make right.

1. Natural law is a standard for lawmakers and citizens, not a license for judges. The conservative worry about activist courts is correct, and the tradition agrees with it. Aquinas assigned the making of human law to those who have care of the community, not to whichever official is most confident in his moral views. The American framers wrote the natural law into the Declaration and then built a Constitution of enumerated powers, written text and elected legislatures to apply it. A judge's duty is to enforce the text the people ratified. The natural law tells the people what to ratify.

1. The tradition corrected its own error. Aristotle's natural slavery was answered from within natural law itself. If all human beings share in reason, as the Stoics taught, and if all are made in the image of God, as Scripture teaches and as Made in God's Image, the Idea Behind Every Claim to Human Dignity explains, then no one is a slave by nature. Abolitionists made exactly that argument from the Declaration's natural law premises. The cure for a bad application of natural law was a better application of it.

1. Vagueness at the edges is not vagueness at the core. People disagree about hard cases in every field. They do not seriously disagree that murder, theft and the enslavement of the innocent are wrong. The first principles are as clear as fire burning in Athens and Persia. That rights rest on something deeper than opinion is argued further in Rights Are Not Social Constructs, and Here Is the Answer to That Claim.

What the long road means now

Every generation is tempted to believe that law is whatever the current majority or the current official says it is. The natural law tradition is the inheritance that answers that temptation. It tells the citizen that his conscience is not a private preference but a share in a moral order he did not invent. It tells the ruler that his power has a limit he cannot vote away. And it tells all of us that the rights in the Declaration are not gifts from Washington that Washington can recall.

That is why it matters that the road is unbroken. The same idea, in nearly the same words, appears in a Greek play, a Roman dialogue, a medieval textbook, a Protestant treatise, a colonial pamphlet, the founding document of the United States, and a letter from a jail. That is not coincidence. It is the human mind, in very different times, finding the same truth.

The case in brief

1. Natural law holds that a moral law binds rulers and can be known by reason, a claim first dramatized in Sophocles' Antigone and defined by Aristotle as justice with the same force everywhere.
2. Cicero called true law right reason in agreement with nature, and Paul located it in the human conscience, written on the heart.
3. Aquinas ordered it into eternal, natural, human and divine law and held that a human law contrary to natural law is a perversion of law.
4. Hooker, Grotius, Locke and Blackstone carried it to the Founders, and Jefferson named Aristotle, Cicero, Locke and Sidney as the Declaration's sources.
5. King's 1963 letter used Aquinas to condemn segregation, and positivism's best objection fails because it has no answer to tyranny that is merely legal.

What you can do: read the Letter from Birmingham Jail and the first two paragraphs of the Declaration side by side this week, then take our civics test and teach one young person in your family the difference between what is legal and what is just.