Is-ought problem

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Portrait of David Hume

The is-ought problem is a meta-ethical philosophical concept articulated by David Hume. Hume's argument states that prescriptive statements, also known as moral statements or "ought" statements, cannot be derived from purely descriptive ("is") statements. The implication of the concept: there is no way to justify morality based solely on observational evidence. This type of argument is a form of non sequitur in that the conclusion does not follow from the premises.

Hume's discussion of the concept[edit]

In A Treatise of Human Nature, Hume states:

"In every system of morality, which I have hitherto met with, I have always remarked, that the author proceeds for some time in the ordinary ways of reasoning, and establishes the being of a God, or makes observations concerning human affairs; when all of a sudden I am surprised to find, that instead of the usual copulations of propositions, is, and is not, I meet with no proposition that is not connected with an ought, or an ought not. This change is imperceptible; but is however, of the last consequence. For as this ought, or ought not, expresses some new relation or affirmation, 'tis necessary that it should be observed and explained; and at the same time that a reason should be given; for what seems altogether inconceivable, how this new relation can be a deduction from others, which are entirely different from it. But as authors do not commonly use this precaution, I shall presume to recommend it to the readers; and am persuaded, that this small attention would subvert all the vulgar systems of morality, and let us see, that the distinction of vice and virtue is not founded merely on the relations of objects, nor is perceived by reason."

The is-ought problem is commonly interpreted to mean: we cannot infer what we morally ought to do from purely factual premises. We can't derive an "ought" from an "is." Further reading of Hume gives a different emphasis. Regarding willful murder, he says:

"The vice entirely escapes you as long as you consider the object. You will never find it until you turn your reflection into your own breast and find a sentiment of disapprobation that derives from you towards this action."

In other words, evil isn't a feature of willful murder but in a judgment arising in sentiment. However Hume criticizes those who mistake their own feelings about things like murder for intrinsic qualities of murder.


This objection is a significant obstacle in using logical argument to demonstrate any ethic system based purely on evidence or science. Given the facts "Alice has food", "Bob is starving", "Alice could give the food to Bob", these statements do not in themselves imply "Alice should give food to Bob". Moral systems cannot be based entirely on evidence and reason. They must be abandoned or justified on other grounds such as axiomatic assumptions or non-rational means.

"If God does not exist, and evolution is true, then is would be immoral to help the weak, because this stunts the natural course of evolution by allowing the genes of the weak to continue in the gene pool.[1]"

If evolution is true, it does not follow we ought to follow any particular course of action.

Argument against divine obedience[edit]

Main Article: Is-ought argument against divine obedience

Theists often assume the Bible is the word of God and that thinking implies God should be obeyed:

  1. Holy books contain ethical standards. (descriptive)
  2. Let us assume the holy book is God's true opinion on ethics. (descriptive)

However, from just these premises, we cannot automatically conclude we ought to obey God, because this is a prescriptive statement.

Once the Bible is established as God's word, it is normal for a believer to assume absolute morality exists. However, absolute morality needs to be established separately because God could claim that absolute morality exists without this actually being the case. In other words, God inspiring the Bible does not automatically imply the Bible is true or should be obeyed.

Criticism of secular morality[edit]

Secular morality refers to moral systems that are not based on God or the Bible. Christian apologetics have attacked secular ideas of absolute morality based on reason and evidence alone. Unless the is-ought problem is addressed, absolute morality cannot be justified with only reason and evidence. However, atheists may use an alternative ethical basis, such as intuition, acceptance of cultural norms or dogmatism.

Sam Harris's Scientific Morality[edit]

Main Article: Science can answer moral questions

Sam Harris proposes something like scientific Epicureanism based on moral realism. He claims all moral systems are a concern for life capable of conscious experience. However, the basis for his ethical criteria is an appeal to the majority based on all existing moral systems. The detail for his specific idea of "good" is supported by numerous appeals to emotion and question-begging claims.


False dichotomy between descriptive and prescriptive statements[edit]

Separating statements into descriptive and prescriptive groups is arguably a false dichotomy.

See also[edit]


External links[edit]

  • Alex Dubinsky, Tackling David Hume’s Is–ought Problem, March 3, 2013 [2]
  • The Is / Ought Problem video, Read by Harry Shearer, Scripted by Nigel Warburton, BBC, 18 Nov 2014.