The Open-Question Argument

Moore's argument that goodness cannot be identical to any natural property because such identities always leave an open question.

Definition

The open-question argument holds that for any natural property N proposed as identical to goodness, the question 'is something that is N good?' remains intelligibly open, which Moore took to show that goodness is not identical to any natural property and is instead a simple, non-natural property.

Scope

This topic covers G. E. Moore's open-question argument against ethical naturalism and the long debate it spawned. It explains the argument's structure, its connection to the charge of the naturalistic fallacy, the standard reply that it conflates meaning with property identity, and its modern revival in Horgan and Timmons's Moral Twin Earth thought experiment against synthetic naturalism.

Core questions

• Why does the persistence of an open question seem to block naturalistic definitions of good?
• Does the argument confuse the meaning of moral terms with the identity of moral properties?
• Does it prove too much by also refuting true a posteriori identities?
• How does Moral Twin Earth update the argument against synthetic naturalism?

Key concepts

• open vs. closed questions
• the naturalistic fallacy
• non-natural simple property
• synthetic identity
• Moral Twin Earth

Key theories

The open-question argument

For any proposed analysis 'good = N', a competent speaker can without confusion ask whether something that is N is good, showing the analysis fails and that 'good' names a simple non-natural property.

Moral Twin Earth

Horgan and Timmons argue that intuitions about a twin community using a different natural property show synthetic naturalists cannot secure that moral terms refer to the naturalist's chosen property, reviving the open-question worry.

History

Moore introduced the argument in Principia Ethica (1903), where it underwrote his anti-naturalist intuitionism and dominated metaethics for half a century. After the causal theory of reference appeared to defuse it, Horgan and Timmons (1992) revived its spirit against synthetic naturalism with the Moral Twin Earth scenario.

Debates

Meaning versus property identity

The standard reply is that the open question only shows 'good' and 'N' differ in meaning, not that goodness and N are distinct properties; just as 'water' and 'H2O' differ in meaning while naming the same thing.

Does Moral Twin Earth succeed?

Horgan and Timmons argue reference-based naturalism cannot accommodate genuine cross-community moral disagreement; synthetic naturalists dispute the underlying semantic intuitions.

Key figures

• G. E. Moore
• Terence Horgan
• Mark Timmons
• Richard Boyd

Seminal works

• moore1903
• horgantimmons1992

Frequently asked questions

Is the open-question argument the same as the naturalistic fallacy?

They are closely linked but distinct. The naturalistic fallacy is Moore's label for the alleged mistake of defining good in natural terms; the open-question argument is the reasoning he used to expose that supposed mistake.