The is-ought problem, for those who believe it is an actual problem, is the problem that you can not deduce an ought statement from any number of is statements.

It seems natural for this to lead to a more extreme view.

  1. Due to Occam's razor, "ought"s simply do not exist.
  2. The is-ought problem does not only apply to morality, but also to all rational decision making (i.e. you can not get to the sentence "I ought to survive." or "I ought to be prosperous." or "I ought to pursue pleasure and avoid pain." from is statements), implying by Occam's razor that rational choices do not exist either.
  3. That, therefore, any decision is not inherently better or more rational than any other decision. More precisely, the claim that a decision is better or more rational than another decision has no real world meaning, since the terms "rational" as applied to decisions, or "better", have no real world meaning.
  4. Even if were to define rational decision in such a way as to avoid this problem (for example, in terms of material facts), rational decision making would still have no binding force.

This would imply that although given beliefs can be rational or irrational, the idea that decisions can be rational or irrational is false.

Has any philosopher taken the is-ought problem this far? If so, I imagine that we would be both a moral and existential nihilist.

  • 'This is usually used to support the idea that morality is unknowable, and separate from human ideas of morality.' Well, not in Hume. For Hume morality is purely a product of human nature. We can ascertain 'matters of fact', expressible in 'is' statements. Under certain conditions, which Hume specifies, the reaction to a matter of fact will be an emotional reaction which Hume equates with moral judgement about what we 'ought' to do. The nature of morality is perfectly knowable for Hume, and is set out in Treatise, III, and it is a wholly human phenomenon mediated by sympathy and utility.
    – Geoffrey Thomas
    Nov 20, 2018 at 18:44
  • No decision... Is a decision.
    – Richard
    Nov 20, 2018 at 20:03
  • 1
    Yes :) it's a Japanese proverb. To do nothing... Is an action.
    – Richard
    Nov 20, 2018 at 20:22
  • 3
    There was one philosopher who considered making this argument, but decided not to.
    – IMil
    Nov 21, 2018 at 0:12
  • 1
    @IMil Which one? (EDIT: Oh wait, that was a joke, wasn't it. :P) Nov 21, 2018 at 1:58

3 Answers 3


We need to avoid confusing our oughts. There's "ought" on its own, which is what Hume was talking about, and "ought in order to achieve a goal". If I wish to hear well, I ought to wear my hearing aids. That doesn't mean I ought to wear my hearing aids. If I ought to hear well, then I ought to wear my hearing aids. Therefore, the "ought" doesn't proceed from "is" statements alone, but is either (according to Hume) a non sequitur or based on an existing ought.

This means that it's still possible to make rational decisions, as long as the decision is in a context of knowledge and desired goals. If I want to hear better, and my hearing aids aren't in my ears, then putting them in is a rational decision. If I want to hear better, then hitting myself on the head with my phone is not a rational decision (unless I have another goal that that would serve). Ought I to save more money? If I want to live a little less well now and have more money later (say, after retirement), then yes. If I want to enjoy things more while I'm young, then no. There doesn't have to be a moral context to have a rational decision.


Sextus Empiricus, following Pyrrho, suggests that whenever you can manage to, the right approach to any action is to 'bracket' judgement as to correctness and accept what happens. Obviously this is also a special case of not being attached, and of achieving by being and not doing, so you could consider the Buddhist deduction, and the core of Taoism to offer the same advice in slightly broader forms.

Of course this man was a physician. So he made decisions all the time. His traditional epithet implies that he practiced what would now be called 'evidence-based medicine'. So you can consider this an extreme form of hypocrisy -- except that you should bracket that judgement, and not apply it...


Is–ought problem is a logical fallacy

Consider the following problem: a car has a 60 kW engine, so its top speed is 100 mph. If we want a top speed of 130 mph, the engine ought to be at least 100 kW. How do we know what "ought to be" if nobody tried such an engine? The answer would be that we know the laws of physics and we calculated the new top speed from them. The next question would be: how do we know that our model of physical laws describes reality sufficiently? And the answer is: if we know reality through observation to declare what is, then we could know reality enough to model what ought to be if we had a better engine. Note that we "could" know, that does not guarantee that we would know certainly.

Obviously, we could apply this kind of reasoning to moral problems. For example, a certain percentage of people are stealing because they do not have enough food (a real problem in Hume's time). While humanist philosophers like Rousseau advocated bettering human conditions to cure social ills, i.e. changing the social order to benefit humanity, "evil" philosophers like Hume reverted to skepticism to preserve the status quo.

Since the history of mankind largely repudiates Hume's fallacy by showing that moral betterment of society is possible (i.e. ought to be could be derived from is), we could hold the is–ought problem only as a obsolete sophism, and not as a real problem.

  • How do we know what "ought to be" whether anybody tried anything or not? Why should that depend on the quality of the engine? Of course, you already decided that that is what ought to determine it, but that is as circular as proving the parallel postulate by assuming something equivalent to it. The is/ought problem is in the apparent impossibility of deriving an ought without assuming any other ought.
    – Conifold
    Nov 21, 2018 at 1:04
  • @Conifold Quality of the car is its speed (simplified of course). Faster car is better, therefore "ought to be" . If you know what is an "essence" of the car, then you know what car ought to be. Similarly, if you know what man is, then you should know what man ought to be. Hume's fallacy is that he assumed that we do not know what (society) ought to be, but we know what (society) is now. This is wrong, because either we do not know anything, or we know what is therefore we could calculate what ought to be.
    – rs.29
    Nov 21, 2018 at 8:14
  • @Conifold Consider this: you have a car with certain speed, carrying capacity, safety, reliability, looks, pollution factor ... You know what is, but you decided that this doesn't satisfy your requirements. You need a car that doesn't exist yet, but "ought to be" .
    – rs.29
    Nov 21, 2018 at 8:26
  • There is no "essence" to a car or a man, attaching one to them is just an ought by another name. And you apparently haven't read Hume since he had plenty to say as to what a man or society ought to be. He just did not pretend to derive it from facts alone. This said, "this is wrong" derives from an ought as well, your own. Please read up on the is/ought problem, your current arguments do not even aim at it.
    – Conifold
    Nov 21, 2018 at 21:43
  • @Conifold Btw, if we adhere to Hume's worldview no one would invent anything (either car, plane or computer) because all of those things were "ought to be" at certain point of time. But obviously world doesn't care for Hume's sophistry .
    – rs.29
    Nov 22, 2018 at 8:30

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