Key Arguments

• Rousseau posits 'a fourth, most important of all' kind of law that 'is not graven on tablets of marble or brass, but on the hearts of the citizens,' emphasizing its unwritten, internalized character and ranking it above the other three kinds.
• He asserts that 'This forms the real constitution of the State,' suggesting that the effective, operative constitution is constituted by shared morals and opinions rather than the formal legal text.
• He describes its dynamic role: it 'takes on every day new powers, when other laws decay or die out, restores them or takes their place,' portraying it as a regenerative force that supplements, revives, or substitutes for positive law.
• He further states that it 'keeps a people in the ways in which it was meant to go, and insensibly replaces authority by the force of habit,' attributing to it both a guiding function and the capacity to transform external compulsion into internalized, habitual compliance.
• He explicitly identifies this fourth law as 'morality, of custom, above all of public opinion; a power unknown to political thinkers, on which none the less success in everything else depends,' highlighting both its neglect in political theory and its foundational importance for all political success.
• He explains that 'With this the great legislator concerns himself in secret, though he seems to confine himself to particular regulations,' indicating that a true lawgiver’s primary, though hidden, work is on morals and public opinion rather than on explicit statutes.
• He concludes with an architectural metaphor: 'for these are only the arc of the arch, while manners and morals, slower to arise, form in the end its immovable keystone,' casting written laws as mere supporting curves and collective morals as the structural element that ultimately holds the whole political order together.

Source Quotes

This gives rise to the setting up of criminal laws, which, at bottom, are less a particular class of law than the sanction behind all the rest. Along with these three kinds of law goes a fourth, most important of all, which is not graven on tablets of marble or brass, but on the hearts of the citizens. This forms the real constitution of the State, takes on every day new powers, when other laws decay or die out, restores them or takes their place, keeps a people in the ways in which it was meant to go, and insensibly replaces authority by the force of habit.

Along with these three kinds of law goes a fourth, most important of all, which is not graven on tablets of marble or brass, but on the hearts of the citizens. This forms the real constitution of the State, takes on every day new powers, when other laws decay or die out, restores them or takes their place, keeps a people in the ways in which it was meant to go, and insensibly replaces authority by the force of habit. I am speaking of morality, of custom, above all of public opinion; a power unknown to political thinkers, on which none the less success in everything else depends.

This forms the real constitution of the State, takes on every day new powers, when other laws decay or die out, restores them or takes their place, keeps a people in the ways in which it was meant to go, and insensibly replaces authority by the force of habit. I am speaking of morality, of custom, above all of public opinion; a power unknown to political thinkers, on which none the less success in everything else depends. With this the great legislator concerns himself in secret, though he seems to confine himself to particular regulations; for these are only the arc of the arch, while manners and morals, slower to arise, form in the end its immovable keystone.

I am speaking of morality, of custom, above all of public opinion; a power unknown to political thinkers, on which none the less success in everything else depends. With this the great legislator concerns himself in secret, though he seems to confine himself to particular regulations; for these are only the arc of the arch, while manners and morals, slower to arise, form in the end its immovable keystone.

Key Concepts

• Along with these three kinds of law goes a fourth, most important of all, which is not graven on tablets of marble or brass, but on the hearts of the citizens.
• This forms the real constitution of the State, takes on every day new powers, when other laws decay or die out, restores them or takes their place, keeps a people in the ways in which it was meant to go, and insensibly replaces authority by the force of habit.
• I am speaking of morality, of custom, above all of public opinion; a power unknown to political thinkers, on which none the less success in everything else depends.
• With this the great legislator concerns himself in secret, though he seems to confine himself to particular regulations; for these are only the arc of the arch, while manners and morals, slower to arise, form in the end its immovable keystone.

Context

Final paragraph of Book II, Chapter XII, where Rousseau introduces and elevates the unwritten 'fourth law' of morals and public opinion, portraying it as the real constitution and the hidden focus of legislative wisdom that ultimately sustains the legal-political order.