Yes, this is essentially the is-ought problem posed as a question. The reason I am asking however, is that I have so far found absolutely no satisfactory arguments for this being the case anywhere that I looked. In fact, this makes me doubt the validity of Prescriptive Ethics as a field in general.

I am hoping that somebody more educated than I can prove me wrong or at least point me to something that I'm missing.

  • Can you give an example of what you're talking about? You mean, 2+2=4 therefore I shouldn't eat meat? Or what?
    – user4894
    Mar 23 '14 at 20:18
  • Generally speaking, yes. "2+2=4 therefore I shouldn't eat meat" is a pretty good example.
    – user5814
    Mar 24 '14 at 5:39
  • Could you give some more specificity. SE is not exactly designed for treatises that cover how to get from 2+2=4 to you shouldn't eat meat. Any such argument would generally require several intervening steps -- any of which could be what you take issue with.
    – virmaior
    Mar 24 '14 at 8:40
  • Actually, don't think I can. Lets just leave it at that for now.
    – user5814
    Mar 25 '14 at 1:45

You can do this if you can demonstrate factually what the purpose of morality is. Let's assume that you can. Then any of these work:


Premise: the purpose of morality is to bring you closer to God. Fact (demonstrated through scripture, let's say): God does not want you to cheat on your wife. Conclusion: It is immoral to cheat on your wife.


Premise: the purpose of morality is to make people happy. Fact (demonstrated through research, let's say): anti-marijuana laws result in more net suffering than does legalization (incl. medical marijuana etc.). Conclusion: criminalizing marijuana use is immoral.


Premise: the purpose of morality is to increase the survival of social animals like us. Fact (demonstrated through modeling, let's say): nuclear weapons pose a threat to our survival. Conclusion: threatening or building capability for thermonuclear war is immoral.

All of these conclusions are moral statements that follow logically from facts, plus an understanding of what the purpose of morality is. If you don't know what the purpose of morality is, or if you successfully argue that there is no purpose to morality, then you're stuck, because you're eternally vulnerable to the "well, I don't feel that way" type of argument.

(Note that there is not universal agreement about what the purpose of morality is, or whether there is any purpose.)


Your question is kind of vague, but you might be asking about moral realism. Here is SEP's preface:

Taken at face value, the claim that Nigel has a moral obligation to keep his promise, like the claim that Nyx is a black cat, purports to report a fact and is true if things are as the claim purports. Moral realists are those who think that, in these respects, things should be taken at face value—moral claims do purport to report facts and are true if they get the facts right. Moreover, they hold, at least some moral claims actually are true. That much is the common (and more or less defining) ground of moral realism.

As a side note, I don't think you meant to say "prescriptive" (unless I've greatly misunderstood you), but you might instead have meant "normative".

  • Yes, I think I messed up my terminology. But thanks for answering in spite of that.
    – user5814
    Mar 24 '14 at 3:22

Yes it is possible to derive an ought from an is. Arthur Prior first pointed out the fact that the naturalistic fallacy wasn't a fallacy in a book called "Logic and the Basis of Ethics" which is from the 30s or 40s.

Here's an example:

(1) He is a sea-captain. (2) Therefore, he should do whatever a sea-captain should do.

(2) clearly follows from (1), and yet (1) is a descriptive claim, and (2) a normative one.

Two things to note about this example. First, the concept sea-captain is a functional concept. There is something that sea-captains do, and it is perfectly objective whether some sea-captain is doing a good job as captain.

Second, the fact that the inference from (1) to (2) cannot be proven valid in ordinary first-order logic does not imply that that the inference isn't valid. Obviously, it is. Rather, one should simply say that the logic of normative inferences is just vastly, vastly more complicated than the baby logic everyone learns as an undergrad. This won't be surprising to people that have done graduate work in logic, or people who have done work in linguistics. But all the reasons to think that you can't derive an is from and ought turn out to just be working with a really impoverished logic. Just because you can't prove the fundamental theorem of calculus with arithmetic doesn't mean it isn't true. It just means you need better tools. The same holds true here.

  • Where should I be looking for those tools then? Any reading recommendations besides the book that you mentioned?
    – user5814
    Mar 24 '14 at 8:33
  • I'm not a specialist in ethics, but I would look at plato.stanford.edu/entries/practical-reason and take a look at the bibliography to get started. Further this anthology seems to have papers by most of the major figures. amazon.com/Varieties-Practical-Reasoning-Bradford-Books/dp/… That should get you started.
    – user5172
    Mar 24 '14 at 11:43
  • (1) He-is a sea captain (2) His failure to act in a way which is consistent with the surrounding community's expectations of a sea caption will result in him losing his job (3) Therefore he has incitement, both socially and economically, to fulfil said expectations. No need for an "ought," or any mention of morality to explain the situation there; the naturalistic fallacy still stands by it's nominal descriptor. Mar 25 '14 at 13:13
  • 1
    @KarlDamgaardAsmussen, when we say he ought to do thus and such . . . we don't mean he has a self-interested reason to do . . . Suppose Sal is a suicidal sea-captain who is trying to spend all his money before he shoots himself. Hence Sal has no interest in keeping making money from his job. Now suppose Sal's at the helm of a boat. It is still the case that Sal should pilot the ship the way a sea-captain should, but false that he has a self-interested reason for doing so. Therefore, the two sentences are provably non-equivalent.
    – user5172
    Mar 25 '14 at 18:25
  • Prior's objection to the is-ought problem (your final paragraph) is much more elegant, though admittedly may not satisfy the question here
    – That Guy
    Jul 1 '14 at 6:53

Yes, it is. In fact that's how ethics must be formulated. Once you have purpose of human life defined according to a First Philosophy then you can formulate ethics as deeds fulfilling the life purpose. I always recommend the philosophy of Plotinus as a prime example of how statements of ethics can be coherently derived from statements of philosophy: http://plato.stanford.edu/entries/plotinus/

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