Wednesday, February 26, 2020

A naive argument that ought implies can

It’s just occurred to me that there is a really quick argument for the ought-implies-can principle:

  1. If you do the morally best you can in a situation S, you’ve done everything you ought in S.

  2. You can always do the morally best you can.

  3. So, you can always do what you ought.

I understand “the best” in the weak sense that if there is a tie for the best, then doing any tied action counts as doing the best.

There is one gap. While (2) is true for us in practice, it won’t be true in certain infinitary situations, such as Satan’s Apple. But we do not in fact find ourselves in such situations, so for us, ought does imply can.


Michael Gonzalez said...

This looks really good to me. I have a sneaking suspicion, though, that there's a problem with including "can" in the first premise. I can't put my finger on exactly what the issue would be; but do you think there's any danger of circularity?

Alexander R Pruss said...

I worry a bit that there might be an equivocation in "can" between "best you can" and "can do what you ought", but I don't see the difference.

Heath White said...

Suppose Jabba the Hutt, after a lifetime of crime and depravity, has deadened his conscience a lot. Recently he has tried to reform a little, however. When he has to deal with his latest victims, he no longer tortures them to death. Instead, he just feeds them to the Sarlacc. He is doing the best he can, morally.

Is he doing what he ought?

Dagmara Lizlovs said...

Feeding some one to the Sarlacc is torturing them to death.

Dan Lower said...

I think for the sake of argument one has to assume that it doesn't, lore to the contrary :/

Alex, can you explain why you said "morally morally" in premise 1 above? I admit I'm confused by this.

Alexander R Pruss said...


Your objection may be right, but let me try to respond.

Your story requires not mere deadening of conscience, but actual destruction of freedom.

Imagine another Hutt, Jolly the Hutt. Jolly was brainwashed to the point where he cannot but kill his enemies. But he has a choice as to how to do so, and he believes the Sarlacc is the least painful way. I think Jolly is praiseworthy for doing the best he can.

But Jabba may be in exactly the same state as Jolly. (In fact, Jolly might have just had Jabba's character superimposed on his brain.) So I think Jabba is praiseworthy for doing the best he can.

Now, Jabba, unlike Jolly, can be blamed for having got himself into a state where his best is so heavily limited.

Alexander R Pruss said...


Because I was in a hurry and I typed the word twice. :-)

Unknown said...

Do you think that the principle 'ought implies can' can undermine modal fatalism?

Alexander R Pruss said...

Yes, I think this is one of the things Kant is right about.