Is there any ethical system wherein all obligations are prohibitions against an action?

So, thou shalt not kill. But never, help those in need of it, or be kind to those you have been unreasonable to, or be fair, or just do unto others.

  • 1
    "Everything which is not forbidden is allowed" is a principle of English common law, but such a thing is more suitable for a legal (and, perhaps, minimalist moral) system rather than an ethical one. The point of ethics is to give some guidance as to what to do, ruling out some behaviors leaves that wide open and defeats the purpose. Something would have to fill the void, the "radical freedom" of existentialists if nothing else.
    – Conifold
    Sep 5, 2019 at 3:10

1 Answer 1


From the point of view of deontic logic, "it is obligatory that" and "it is permissible that" are definable in terms of each other; one of them is redundant. This implies that for any ethical system, any "positive" obligation can be transformed into a prohibition (a statement of the form "it is not permissible that...") like so:

"It is obligatory that you do P" becomes "it is not permissible that you not do P".

"Help those in need" can be stated as a prohibition, as "it is prohibited to not help those in need".

So, to answer your question, I think any ethical system whatsoever of positive obligations can be converted into a logically equivalent system of prohibitions.

  • surely there's a different between not acting to help those in need and the act of murder?
    – user38026
    Sep 3, 2019 at 16:21
  • @another_name There is, but either of those can be converted into a prohibition or a positive obligation. "Help those in need" can be stated as a prohibition: "it is prohibited to refrain from helping those in need". And the prohibition of murder can be stated as a positive obligation: "One ought to not kill". My point was that I don't think there is a a real distinction between positive obligations that tell one how to act, and negative prohibitions that tell one how not to act, since they always seem to be convertible into the other. Sep 3, 2019 at 16:45
  • ah ok that wasn't all i was asking about in the question: was it unclear?
    – user38026
    Sep 3, 2019 at 17:08
  • The standard deontic logic, with the P=~O~ rule, is well-known for its paradoxes, and other deontic logics do not adopt this rule. Just because it is handy to adopt a formal rule in a crude model does not mean that it matches reality. In ethics, actions and omissions are usually distinguished, and so are different types of obligations and permissions.
    – Conifold
    Sep 3, 2019 at 17:59
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    SEP Challenges to Standard Deontic Logics. See also Hansen's Ten Philosophical Problems in Deontic Logic, that discusses negative and positive permissions specifically:"Von Wright, in his late work starting with [61], dropped the concept of inter-definability of obligations and permissions altogether by introducing P-norms and O-norms... von Wright’s new theory means that in the absence of explicit P-norms only what is obligatory is permitted..."
    – Conifold
    Sep 3, 2019 at 19:30

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