The is/ought gap
The is/ought gap is the observation in philosophy that facts are separate from values. Judgements of value, as in moral or aesthetic judgements, cannot be determined true or false in the same way as statements of fact.
The gap is important in metaethics, as some moral systems attempt to deny or circumvent the boundary. Some moral objectivists invoke a supernatural being to universalize their values, whilst moral realists collapse the boundary by attempting to show that at least some values are embedded in facts.
Hume's Law
The gap was noted by David Hume in his A Treatise of Human Nature (1739-40). Hume points out that some philosophers mistakenly transition from “is” statements—what Hume describes as “the ordinary way of reasoning”—to “ought” statements in the course of their arguments. Hume points out that this is a fallacy. “It is necessary,” he explains, “that [ought-statements] 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.” [1] Hume takes this as further evidence of his belief that morals are not discoverable by reason.
Hume's Reasoning
Hume’s comments on the is-ought gap appear in his book at the end of the section “Moral Distinctions Not Derived from Reason.” Throughout this section, Hume is concerned with whether it’s true, as some philosophers contend, that morals are universal and accessible like matters of fact to reasoning human beings. The problem for Hume is that reason and morality are inescapably different. For Hume, reason is an operation of the mind that has no influence on actions. It’s a tool for discovering truth or falsehood, for coming to agreements or disagreements about the relations of ideas or matters of fact. It can neither approve of or disprove of actions; it can only compare and describe. Conversely, morals are instructions for producing or preventing actions. Because morals directly influence behavior, Hume confines morality to the world of sentiment and feeling, and concludes that the merits we ascribe to actions arise from our passions, not our faculty for reason.
Hume entertains a number of thought experiments demonstrating some of the absurdities that arise when morality is based in reason or construed as factual. For example, he points out that there is no reason why the actions of any creature or object couldn’t also be couched in moral judgements. He describes the parricide that arises when the seed of an oak tree grows up and destroys the parent oak tree. It doesn’t matter for Hume that the seedling couldn’t have intended parricide like a person can. The causes and effects are the same; the sequence of events that constitute the parricide is understandable and describable in factual terms, but we have to look elsewhere, i.e., to the world of human conventions, in order to construe the event as parricide.
| Statement of the claim | The is/ought gap |
| Level of certainty | Proven |
| Nature | Factual |
| Counterclaim | Denial of the is/ought gap |
| Dependent on |
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| Dependency of |
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