Some time ago, I've read a principled argument about how to fully legislate ethics is pragmatically impossible and also itself unethical (this seems like a contradiction, but the relationship between law and ethics was sufficiently explored for it to work).

The argument applied to very uncontroversial ethical rules – not issues people are divided about, e.g. abortion, selling psychotropic substances, meat eating etc.

It tried to show how fundamentally different criminal law and punishment works compared to ethics, and that this is an in-built “feature” or “defect” of law which cannot be avoided.

Sadly, I've forgotten who wrote it and I've also forgotten the details, so I'm not going to repeat it here, it would only be a crude caricature of the original subtle argument.

In my search to find this or similar arguments, I've found a lot of commentary on the issue, but this was all very general, based on examples – mostly regarding those controversial issues – and sentiments rather than rational argumentation which gets to the core of the question.

Does anybody know principled arguments that try to prove that “you cannot legislate morality” (pragmatically and/or ethically)?

  • The nature of the mentioned argument is hard to tell. One principled argument against "legislating morality" comes from the separability thesis of legal positivism. But even under an opposing position, like Devlin's legal moralism, one does not legislate morality "fully", it just is permissible to legislate some socially shared values.
    – Conifold
    Jul 3, 2017 at 20:34
  • @Conifold and the ethical part argued in the direction that even if such laws could work, we remove the freedom to behave ethically, which is itself unethical (it was rigorously justified, but sadly I just forgot the details).
    – viuser
    Jul 3, 2017 at 23:03
  • @Conifold the pragmatic part went along that way (crude caricature): criminal law can only prohibit certain acts. Except for extreme cases never compel people to active ethical acts. We naturally built connections with other people by behaving ethically, if law compels us to be for example grateful, it can't either define how strong the gratefulness should be, or it sets an arbitrary standard of minimal gratefulness which then becomes “calculated” into the whole thing, so that additional gratefulness is needed for truly grateful people, and so the law is constantly missing its goal.
    – viuser
    Jul 3, 2017 at 23:09
  • It's really hard to guess just based on the description, but Kant also distinguishes between what a state should make illegal (certain types of actions) and what is immoral (anything that fails CI).
    – virmaior
    Jul 3, 2017 at 23:32
  • 2
    This is the theme of the Metaphysics of Morals and is explained its preface -- also in the preface to Metaphysical Principles of Justice [Rechtlehre] (which is part of the Metaphysics of Morals) -- n.b. this is not Groundwork of the Metaphysics of Morals
    – virmaior
    Jul 4, 2017 at 4:46

2 Answers 2


The legal enforcement of morality - external behaviour

If one confines morality purely to external behaviour - i.e. to behaviour that can be done whether one thinks one ought to do it or not - then morality can be enforced. For instance, if it is a moral requirement not deliberately to short-change customers, then the law can take effective action against anyone who does this and threaten and practise enough superveillance and apply sufficient penalties to deter anyone who contemplates this form of dishonest behaviour. At least something close to this, and counting as the enforcement of morality, can be done.

In the USA and UK until well into the 20th century gay acts - even 'homosexual conduct' in private - was subject to legal prohibition on moral grounds. Nor was the law inactive. Anti-gay morality was definitely enforceable - and enforced in regard to these 'grossly immoral acts', as the judiciary was apt to call them.

The legal enforcement of morality - internal motivation

However, if one builds into one's understanding of morality the motivation behind behaviour then the enforcement of morality looks far more problematic. The law can through surveillance and prospective penalty stop me from cheating my customers but it cannot make me independently want to deal honestly with them. It can control my actions through coercive incentives or enticing appeal to to self-interest, but it cannot instil the motivation to deal honestly because I think this is the right thing to do. If so, then neither the law nor any other social agency can make me act from a sense of duty, a sense of what I ought to do regardless of the coercive incentives or appeal at play.

In this sense of morality, in which a motivation of duty or obligation in involved, it is impossible to enforce morality.

Enforcement of external behaviour which violates internal motivation

Since this is so, it is hard to be clear how it could be unethical to enforce morality - if it can't be done, it can't be unethical to do it. But perhaps some sense can be given to the notion. It is, within certain limits, unethical to enforce external behaviour which violates people's internal motivation - their sense of right, duty, obligation and conscience. Legislation in the USA and the UK during the two world wars brought in conscription - a non-voluntary legal requirement to serve in the armed forces. Yet there was also a recognition of the legitimacy of conscientious objection. External behaviour which violated internal motivation was possible but was judged unethical.


One argument is that law should be plain and definite and objective. Ideally, I should know if I'm breaking the law, presumably so I can avoid breaking it. There are very few shades of behavior legally: either you're innocent, or you're guilty of one of a few offenses. The decision of whether I broke the law should be based on objective evidence, such as my actions, although there are distinctions based on more subjective things (the difference between first-degree and second-degree murder in the US is whether the killing is an impulse or a deliberate decision).

Topics of morality are much fuzzier. First, we don't all have the same moral principles. Some people consider homosexuality a sin, while I think it's just another form of sexual behavior. Second, we don't have to make hard decisions on individual actions. It's perfectly reasonable to consider an act of mine as being around the border of immorality, or to be unable to decide. Third, we can go into as much detail as we like in evaluating morality, including subjective reasons. Fourth, deciding if something is immoral doesn't carry nearly the same penalties as deciding that something is illegal, so laws have much more deterrence.

Therefore, laws have to be relatively simple and specific, compared to morality. They have to be more or less objectively determinable, unlike morality. They have to be something a majority can agree on. We don't want laws to be too far-reaching, so that they penalize too many moral actions.

Clearly, laws have to be based on some sort of morality. We forbid murder and various other crimes because we think them immoral. Equally clearly, they can't try to ban too much immorality. Laws that infringe on freedom of speech can have a chilling effect that suppresses people's speech in various areas. The best balance seems to be to have laws that cover mostly immoral behavior, and have things like prosecutorial discretion and pardons to cover the case of the illegal moral action.

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