Concept
Ought implies can
Overview
"Ought implies can" is an ethical formula ascribed to Immanuel Kant that claims an agent, if morally obliged to perform a certain action, must logically be able to perform it: For if the moral law commands that we ought to be better human beings now, it inescapably follows that we must be capable of being better human beings.
The action to which the "ought" applies must indeed be possible under natural conditions.
Kant believed this principle was a categorical freedom, bound only by the free will as opposed to the Humean hypothetical freedom ("Free to do otherwise if I had so chosen"). There are several ways of deriving the formula—for example, the argument that it is wrong to blame people for things that they cannot control (essentially phrasing the formula as the contrapositive "'cannot' implies 'has no duty to'").
This ethical formula can be expressed in deontic logic with the multimodal axiom:
O
A
→
◊
A
{\displaystyle OA\to \Diamond A}
, where the deontic operator
O
{\displaystyle O}
means "It's obligatory that..." and the alethic operator
◊
{\displaystyle \Diamond }
means "It's possible that...". However, in practical situations, obligations are usually assigned in anticipation of future events, in which case alethic possibilities can be hard to judge; Therefore, obligation assignments may be performed under the assumption of different conditions on different branches of timelines in the future, and past obligation assignments may be updated due to unforeseen developments that happened along the timeline.
By the contrapositive, the logical equivalent of "ought implies can" is the formula
◻
¬
A
→
¬
O
A
{\displaystyle \Box \neg A\to \neg OA}
, which means "impossible implies omissible".
Overview adapted from Wikipedia (CC BY-SA 4.0; see the article history for authors).
Possible passages
Found by search and not yet checked by a person; they may only mention the idea in passing.
In the former case, however, the law has the form of an imperative, because in them, as rational beings, we can suppose a pure will, but being creatures affected with wants and physical motives, not a holy will, that is, one which would be incapable of any maxim conflicting with the moral law. In their case, therefore, the moral law is an imperative, which commands categorically, because the law is unconditioned…
Immanuel Kant, The Critique of Practical Reason
States what Ought implies can is; the author is tied to Ought implies can in the knowledge graph.
Philosophy must then assume that no real contradiction will be found between freedom and physical necessity of the same human actions, for it cannot give up the conception of nature any more than that of freedom. Nevertheless, even though we should never be able to comprehend how freedom is possible, we must at least remove this apparent contradiction in a convincing manner. For if the thought of freedom contradicts…
Immanuel Kant, Fundamental Principles of the Metaphysic of Morals
The author is tied to Ought implies can in the knowledge graph.
The only particular in which any one can differ, is, that either, perhaps, he will refuse to give the name of necessity to this property of human actions: But as long as the meaning is understood, I hope the word can do no harm: Or that he will maintain it possible to discover something farther in the operations of matter. But this, it must be acknowledged, can be of no consequence to morality or religion, whatever…
David Hume, An Enquiry Concerning Human Understanding
States what Ought implies can is; the author is tied to Ought implies can in the knowledge graph.
Related ideas
Opposing perspectives
Place in the tradition
Part of Deontic logic.