If you want to understand the moral basis of a free society, there might be no better place to start than the thought of Immanuel Kant. He is the most significant and widely discussed moral philosopher in history. And he was self-consciously an Enlightenment liberal who believed in limited government and maximum freedom.
Let’s take a look at the elements of his moral and political argument for freedom.

I. The Good Will and the Moral Law

In his first work of moral philosophy, The Foundations of the Metaphysics of Morals, Kant tries to systematize our common moral intuitions in order to give us a method for deciding moral controversies — that is, issues where our consciences or intuitions might disagree with others’ or not speak clearly.



He notes that the only unconditionally good thing in the world, according to common understanding, is a good will. Good fortune, health, and even happiness broadly understood are not unconditionally good, because when married to a bad will they become a source of condemnation for an impartial spectator. We don’t applaud the evil man who achieves his goals and rides off into the sunset savoring his victory. We condemn him and hope his plans are frustrated. No, more important than being happy is to be worthy of happiness, that is, to have a good will.
On this point, the Objectivist founder Ayn Rand misinterpreted Kant. She believed he was what she called an “altruist,” who thought it was praiseworthy to sacrifice happiness. Kant believes, as most of us do, that happiness should not motivate us to the exclusion of duty. Obedience to the moral law — duty — is the most important thing, but happiness is also desirable.
Kant notes that an important assumption necessary for moral responsibility is the idea that we human beings give the moral law to our own wills. We say to ourselves, “This is the right thing to do, and so I will do it.” We don’t know how it is possible for us to freely determine our own wills, but it must be possible for us if we are to consider ourselves as morally responsible beings.

II. The Categorical Imperative

The moral law takes the form of an unconditional or categorical imperative. It says, for instance, “Do not murder, even if you can achieve your goals by doing so.” It’s not a hypothetical imperative like “if you don’t want to burn your hand, don’t touch the hot stove,” or “if you don’t want to go to jail, don’t murder.” It commands our wills regardless of what our particular goals are.
Kant thinks all particular moral commands can be summed up in a fundamental, categorical imperative. It takes three forms. I’ll mention two of them here.
One form of the categorical imperative focuses on the notion that human beings are special because of our capacity for moral responsibility. Kant assumes that this capacity gives each individual human being a dignity, not a price. What that means is that we must not trade off the legitimate rights and interests of any human being for anything else. We must not treat other people or ourselves as means only to some other end, but always as ends in ourselves.
The other, perhaps more frequently cited, form of the imperative is highly abstract: “Always act according to that maxim that you can will as a universal law of nature.” In other words, think about the principle or rule that justifies your action; then figure out whether it’s universalizable. If so, it is an acceptable principle or rule for you to follow; if not, it is not. “Steal when I can gain an advantage thereby” is not universalizable because it implies that others may steal from me, that is, take what I own against my will. But I cannot will against my own will.

III. Rights and Freedoms

Now, this understanding of the dignity of the individual human being implies that persons have rights, in other words, that we have an enforceable duty to respect the freedoms of all persons.
So we can’t trample on the freedoms of one person to help one or many others (contra the “act utilitarians”). For instance, it would be wrong to kill one healthy person to distribute her organs to several sick people, even if doing so was necessary to save two or more lives. Each person has a dignity that must not be trampled, no matter what.
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(Another misunderstanding of Kant says that he thinks your intentions are the only thing that matter and you can ignore the consequences of your actions. To the contrary, to ignore consequences is to act with ill intent. Consequentialists differ from Kant in believing that only aggregate consequences of actions need be taken into account. Kant’s political theory is individualist, while consequentialist theories are inevitably collectivist.)
In an essay titled “Theory and Practice” (short for a much longer title), Kant gives an overview of his political theory. Once a civil state has been established to secure our rights, he says,
No one can compel me to be happy in accordance with his conception of the welfare of others, for each may seek his happiness in whatever way he sees fit, so long as he does not infringe upon the freedom of others to pursue a similar end which can be reconciled with the freedom of everyone else within a general workable law — i.e. he must accord to others the same right as he enjoys himself.
Kant therefore endorses the law of equal freedom, that everyone should have maximum freedom to pursue happiness consistent with the like freedom of everyone else, or what some libertarians have called the “Non-Aggression Principle.” This principle applies under government, not just in the state of nature.
The equal freedom of each subject in a civil state, Kant says, “is, however, perfectly consistent with the utmost inequality of the mass in the degree of its possessions, whether these take the form of physical or mental superiority over others, or of fortuitous external property and of particular rights (of which there may be many) with respect to others.” Kant is no Rawlsian; he is a classical liberal who realizes that liberty upsets patterns and should be preserved in spite of (or because of) that.
In the same essay, Kant endorses Locke’s view of the social contract. A legitimate state with a right to rule can emerge only after unanimous consent to the initial contract. To do otherwise would be to violate the non-consenters’ rights. We now know that unanimous consent to the social contract has rarely occurred in human history, and so Kant’s strong theory of individual rights sets us up for a rejection of political authority.
If we reject political authority, the largest state we can possibly justify is a minimal state, and, according to some, not even that.

IV. Kantian Liberalism

Kant’s moral philosophy justifies extremely strong individual rights against coercion. The only justification for coercion in his philosophy seems to be defense of self or others. His ideal government therefore seems to be extremely limited and to allow for the free play of citizens’ imaginations, enterprise, and experiments in living.
Kant does take some strange positions on particular moral positions. He has an odd view of marriage as a kind of mutual servitude, he denies that there is a right to resist an unjust sovereign, and he thinks lying is always wrong, no matter what. I find that Kant is most persuasive at his most abstract, when he deals with fundamental philosophical issues.
Whatever your opinion of his work, Immanuel Kant deserves to be widely read by classical liberals and libertarians. His contributions to liberalism are important and still underappreciated.