Moral law

A standard of conduct binding on everyone, holding whether or not any legislature has enacted it.

Theme: Ethics and character
Tradition: Cross-tradition
Term fixed: c. 1270

In plain terms

Some things seem wrong regardless of what the law of the place says. If a legislature enacted that a category of people may be killed, the enactment would not make it permissible - it would make the law wrong.

That intuition is what moral law names: a standard above statute, which statutes can fail to meet and against which they can be judged.

The difficulty is saying where it comes from and how anyone reads it. If it is written into nature, we need an account of how a fact about nature obliges anyone. If it comes from God, then non-believers are outside it, or it holds for reasons that do not depend on belief - in which case the reasons are doing the work. And if it comes from reason alone, it has to be shown that reason really does deliver a content and not just a form.

As a philosopher would put it

Aquinas's natural law is the rational creature's participation in the eternal law: its first precept is that good is to be done and evil avoided, and its content is derived from natural inclinations - to self-preservation, to the raising of offspring, to knowledge and to society. Human law derives from it, and an unjust law is a corruption of law rather than a law.

Kant relocates the source. The moral law is not read off nature but given by practical reason to itself; the categorical imperative is its formula, and autonomy consists in being subject to a law one legislates. That removes the dependence on theology and on any account of natural ends.

The positivist reply, from Bentham through Austin to Hart, separates law from morality: what the law is and what it ought to be are different questions, and calling an unjust rule not-law confuses them. Hart's exchange with Fuller in 1958, prompted by the postwar German cases, is the classic statement of both sides.

Where you meet it

The charter of the International Military Tribunal at Nuremberg made crimes against humanity punishable whether or not they violated the domestic law of the country where they were committed.

That clause is the point of philosophical interest. Much of what was charged had been lawful under German statute at the time; the defence argued that punishing it retroactively violated the principle that there is no crime without a prior law. The tribunal's answer was that the acts were criminal by a standard that did not depend on enactment, and that the perpetrators knew it.

After the war German courts faced the same question domestically, in cases where informers had denounced people under laws that were valid and monstrous. Gustav Radbruch's formula - that positive law must yield where its conflict with justice reaches an intolerable degree - was formulated in response and has been applied since, including to the border guard cases after 1990. It is natural law reasoning used by courts that would rather not have needed it.

What is actually disputed

Whether there is any law above enactment.

Positivists argue that the separation of law and morality is what makes criticism of law possible: calling an unjust rule not-law removes the vocabulary for saying that a valid law is wicked and should be disobeyed. Hart's charge is that natural law obscures the issue at exactly the moment clarity is needed.

Natural lawyers reply that a purely formal account of validity gave the twentieth century's worst regimes their defence, and that Radbruch's formula names something courts actually needed and used.

The deeper problem is content. Even granting a law above statute, its provisions have been read very differently across time - natural law has been invoked to justify slavery and to abolish it, to defend hierarchy and to overthrow it. A standard that yields opposite answers to its most confident readers is doing less work than its defenders claim.

Commonly confused with

the laws of nature in physics Physical laws describe what happens. Moral law says what ought to happen and is not falsified by being broken.
divine command Natural law in Aquinas is knowable by reason without revelation, which is why he thought it bound everyone.
Conscience c. 397 Conscience is the faculty that applies a standard. The moral law is the standard, and a mistaken conscience is possible on any natural-law account.

Defined against

Is–ought gap If no ought can be derived from any is, then a law written into nature has no route from the fact to the obligation

Philosophers

Thomas Aquinas Natural law systematised, with human law derived from it
Immanuel Kant The moral law given by reason to itself
Cicero The Stoic law of nature, in its most influential ancient form
Jeremy Bentham The attack on natural rights as nonsense upon stilts
Marcus Aurelius Law as reason common to all, in a Stoic register

Works

Summa Theologiae The systematic account of natural law
Groundwork of the Metaphysics of Morals The moral law grounded in reason
An Introduction to the Principles of Morals and Legislation The utilitarian and positivist alternative
Meditations The Stoic version, in practice
Leviathan Law as the sovereign's command, against the higher-law tradition

Schools

Thomism Where natural law is systematised
Natural Law The tradition named for it
German Idealism Where its source becomes reason
Classical Utilitarianism Where it is rejected as fiction
Early Stoicism Where the ancestor idea is formed

Related concepts

Duty 1785 · Justice c. 380 BC · Rights 1689 · Conscience c. 397 · Autonomy 1785

The Stoic idea of a law of nature identical with reason is the ancestor; Aquinas gives it the systematic form later law has argued with, and Kant relocates its source from nature to reason itself.