As far as I understand, the well known Kant's principle "Ought implies can" means: if you are morally obliged to do X, then you ought to do X. And (as explained here: http://web.mnstate.edu/gracyk/courses/phil%20318/ought-can_Outline.htm) if you can't do X you are not morally obliged to do X. Which makes sense to me. The problem is that, to me, the slogan "Ought implies can" means: if you are morally obliged to do X, then you can do X. In my opinion this last implication is false (the fact that you should do X does not imply that you actually can do so); so it'd make more sense if the quote was "can implies ought": if you can do X and you are morally obliged in doing X, then you ought to do X.

P.S.: I'm pretty sure this is 90% due to the fact that I'm not a native English speaker.

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    "Ought implies can" does mean that to be morally obliged to do something one must at least be physically capable of doing it. In other words, morality does not impose impossible demands. Whether it seems right or not Kant endorsed it, if one can not do something (not in the colloquial sense of "really does not want to" but physically) their moral duty thereby excludes it.
    – Conifold
    Sep 10, 2020 at 17:32

3 Answers 3


"Ought implies can" means that if you can not, in fact, do something, you are not, in fact, obliged to do something, and therefore, to say that someone ought to do something implies that the person can do it.


Two of the most famous (or at least known-by-me) uses of ought-implies-can work exactly as you don't think they should. The first is Anselm's argument for the Incarnation:

Only God can atone for sin. Only humanity ought to atone for sin. Therefore, there can be a being who is both God and man, without confusion or conflation.

Or Kant says: when you do something wrong, it was possible to not do so; ergo we have choices between possibilities.

Rawls mentions the precept in connection with the abstract threat of intolerant cults amassing weapons, saying there could be instances of the cult posing such a danger that we might waive ought-implies-can as a defense of something, here, but besides being peculiar, the example is legal, not metaphysical.

PS: there's also "the logical necessity of obligation" puzzle (see McNamara's article in the SEP). Deontic logic doesn't seem absolutely "free," but one standard principle says that there is a logically necessary obligation to metaphysically uphold the law of noncontradiction. This has been taken to require the existence of beings who can fulfill the obligation, which you might interpret theistically (only God can "uphold" something like the LNC) or as some perpetual order of agents; but usually the hope is to solve the puzzle with a "free logic" conclusion.


The very idea of "ought" itself implies the possibility of choice by a free will, as opposed to some other choice. Thus it stands apart from purely mechanical causality. Where no freedom of will exists the "ought" does not exist or cannot be properly applied.

We may say that the dog who eats the sandwich on the kitchen counter, ought not to have done that and is a "bad dog!" But we do not grant the dog moral choice and free will, at least not same degree as those of us with self-reflection and the moral example of the Son of God.

The dog is, as Pavlov would demonstrate, at least partly "mechanical," though not perhaps a Cartesian automaton. Our application of "ought" to the dog is merely anthropocentrism and whimsey. A behaviorally conditioned human is another matter, and I don't think Kant every contemplated or would ever accept humans "beyond freedom and dignity," except as the most horrible injustice.

So free will is required for any "ought." But free will requires worldly traction and can't simply skate around in our frictionless daydreams. Without the possibility of action, the moral exercise of free will cannot be exercised. Not to achieve goals per se, but to prove to itself its true intent.

Unlike existentialists, Kant may be willing for forego the imperative of actualized choice, I'm not sure about that. But where there is no possibility of a free action, the "ought" does not come into play. We are simply locked into the gears of the mechanical universe. The "can" is part of what is meant by "ought."

It is notable that the "ought" of Kant's CI is generally considered too empty of content for too many real-world cases. And it is illustrated by negation through actions, such as lying, that you "ought not" to do. The moral law applies in the realm of possibility, as presented to the life of the individual Protestant soul, the synthetic a priori realm where things can be done.

So, interestingly, Kant probably saw no moral duty to do all in his power to free the American slaves, though arguably within his maxim, whereas a utilitarian like Singer would, and in that sense seems more "universal." This may be a strike against against Kant's blend of Enlightenment liberalism and Christian universalism, a specter that still haunts liberalism.

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