The Naturalistic Fallacy and the Is-Ought Gap

Two classic obstacles to deriving moral conclusions from purely factual or natural premises.

Definition

The is-ought gap is the claim that no set of purely descriptive ('is') premises logically entails a normative ('ought') conclusion; the naturalistic fallacy is Moore's alleged error of identifying or defining the moral property goodness with a natural property.

Scope

This topic treats two related but distinct doctrines often run together. Hume's is-ought (or fact-value) gap is the logical thesis that one cannot validly derive an evaluative or normative conclusion from purely descriptive premises. Moore's naturalistic fallacy is the metaethical charge that it is a mistake to define a moral property in terms of any natural property. The topic clarifies the difference, surveys attempts to bridge the gap, and assesses their bearing on naturalism.

Core questions

• Is it logically impossible to derive 'ought' from 'is'?
• Are the is-ought gap and the naturalistic fallacy the same doctrine?
• Do institutional facts or thick concepts bridge the gap?
• If the gap holds, what follows for ethical naturalism and for moral knowledge?

Key concepts

• is-ought gap
• fact-value distinction
• naturalistic fallacy
• institutional facts
• thick concepts

Key theories

Hume's is-ought thesis

Hume observed that moralists slide from 'is' and 'is not' to 'ought' and 'ought not' without explanation, suggesting that evaluative conclusions cannot be deduced from purely factual premises.

Moore's naturalistic fallacy

Moore charged that defining good in terms of any natural property commits a fallacy, since goodness is a simple, non-natural, indefinable property revealed by the open-question argument.

Searle's derivation

Searle argued that from the institutional fact that someone made a promise one can derive that they ought to keep it, claiming to bridge the gap via constitutive rules of institutions.

History

The is-ought observation appears in Hume's Treatise (1739) and was elevated into 'Hume's law' by later readers. Moore's Principia Ethica (1903) introduced the separate naturalistic fallacy. Twentieth-century debate, including Searle's 1964 derivation and work on thick concepts, probed whether and how the gap might be bridged.

Debates

Whether the gap can be bridged

Searle and others argue institutional and constitutive facts yield genuine 'ought' conclusions; critics reply that such derivations smuggle in an evaluative premise or only yield institutional, not categorical, oughts.

Distinguishing the two doctrines

Conflating Hume's logical gap with Moore's semantic fallacy causes confusion; a naturalist can accept the is-ought gap while rejecting the naturalistic fallacy by treating moral-natural identities as synthetic.

Key figures

• David Hume
• G. E. Moore
• John Searle

Seminal works

• hume1739
• moore1903
• searle1964

Frequently asked questions

Are the is-ought gap and the naturalistic fallacy the same thing?

No. The is-ought gap is a logical claim about what can be deduced from descriptive premises; the naturalistic fallacy is a semantic-metaphysical claim about defining moral properties. They are often run together but are logically independent.