My intuition seems to say yes, however I'm not quite sure how to go about reasoning about this. I'm particularly interested in evaluating this using the first and second categorical imperative.

I assume that when attempting to formulate a universal maxim it would result in something like 'it is permissible prevent unethical action against ones self'. Do we need to add a caveat to the maxim to consider whether the preventative action take is itself ethical or unethical? Or does that not matter? There doesn't appear to be any immediate contradictions, but I'm not sure what direction to take from here.

Additionally, if the caveat is necessary, then does that mean that from the Kantian view, if no ethical prevention/avoidance is possible, we're ethically obligated to just 'sit back and take it'?

  • 1
    A maxim needs to include the means taken, and I think there are problems with preemptive attacks in general (How should one be sure what's going to happen? Kant is very cautious regarding this). These things are to be considered and the reason why self-defense is only legally allowed against current, actual attack and only for reasonable and necessary amounts of force imho.
    – Philip Klöcking
    Oct 1, 2017 at 23:25
  • True, however the situation I had in mind was a bit more benign and while preemptive, not necessarily an attack, as I was attempting in a paper I wrote to relate this to ad-blocking. I was hoping for a line of logic along the lines of if the (above) is ethical, then proving online ads unethical would prove ad-blocking ethical. Then I realized it wasn't quite that simple, and wondered if a generalization was possible, hence the question.
    – Asmodean
    Oct 1, 2017 at 23:42
  • You're very limited trying to prove another's actions to be unethical with Kant. As the illustration of the shopkeeper shows, it is the intention that makes an act moral, and you cannot possibly know the intention of another. Only if their actions have directly transgressed the categorical imperative could you say with some certainty they were acting unethically. Such situations are rare in real life and even then you may be making some unwarranted presumptions about their intent.
    – user22791
    Oct 3, 2017 at 6:31

1 Answer 1


There's several reasons to believe Kant would not

  1. include a duty to prevent another person's unethical actions


  1. consider preventing the action of another person in general moral

First let's start with the distinction between these categories. Type 1 is whether this would fall under the required duties that arise out of the categorical imperative. While Kant supplies several formulations, the important point here is the distinction between perfect duties and imperfect duties (see https://plato.stanford.edu/entries/kant-moral/ and also Marcia Baron, Kantian Ethics almost without Apology). For Kant, perfect duties arise from either

  1. considering what is universally required OR
  2. identifying what is necessary to respect rational beings as ends.

Imperfect duties, in contrast, arise for human rational beings because they at times need things. Thus, we have an imperfect duty to assist others and to develop our talents, because we have at times needed others to act according to maxims that accord with this but not at all times.

To this, we need to join an odd and often over-looked feature of Kant's ethics: that Kant believes we are to assume that humans and other rational creatures act rationally. This is a major motive for his views on lying (prior to the sense in which he thinks it violates a duty to one's self in Metaphysics of Morals).

It's also a mirror image of the Kantian idea that you can do the "right" action but not from the right maxim and thus not have acted morally (Groundwork Section 1 -- discussion of the shopkeeper; n.b. that doesn't mean the shopkeeper acts immorally).

Returning to the question of whether we can have a duty to actively prevent another's unethical actions, we can first ask whether we have a perfect duty to do so. The answer on the Kantian picture is no, because it would make no sense for any rational to have a moral maxim of harming others, so there's no way to have an perfect duty to prevent others from harming since this would never rationally arise.

I want to briefly skip over the potential for an imperfect duty to prevent others from causing harm to state that for Kant, in general, the prevention of the expression of another's will is immoral, because others are assumed to be acting rationally and worthy of respect in our treatment of their wills. This is a strong motive for Kant's view "On a Supposed Right to Lie" in response to a killer where he rejects lying as an option (contra many of his contemporary followers).

At best, I think you could argue we have an imperfect duty -- meaning a duty we can do some of the time -- to prevent others from causing harm. But this would have to be severely qualified. First, it would have to be qualified in the sense that we are not acting to prevent the will of a rational creature, because on Kant's view we should assume a rational creature is trying to act morally. In other words, it would have to be narrowly restricted to obvious wrongs like murder (for which Kant believes there can be no moral maxim).

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    Thanks for the insight; I think I generally follow. Just a clarification: When you say 'obviously wrong things like murder', are you saying that in the sense of 'society thinks it is wrong' or in the sense that it is obviously wrong because the act is clearly violating someone else' will, or something else?
    – Asmodean
    Oct 3, 2017 at 18:24
  • Something is obviously wrong on the Kantian picture if no possible maxim can exist for it. There's no possible maxim that makes a murder, theft, or fraud legitimate. This is because such actions do not respect rationality in others and cannot be universalized. If we accept Kant's view it, it is only coincidentally that 'society thinks it is wrong' (unless that society is perfectly rational in its thinking).
    – virmaior
    Oct 3, 2017 at 22:55

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