Water Is and Is Not H2O

Mind & Language, Forthcoming

34 Pages Posted: 16 Mar 2017 Last revised: 14 Nov 2018

See all articles by Kevin P. Tobia

Kevin P. Tobia

Georgetown University Law Center

George Newman

Yale School of Management

Joshua Knobe

Yale University

Date Written: March 14, 2017


The Twin Earth thought experiment invites us to consider a liquid that has all of the superficial properties associated with water (clear, potable, etc.) but has entirely different deeper causal properties (composed of “XYZ” rather than of H2O). Although this thought experiment was originally introduced to illuminate questions in the theory of reference, it has also played a crucial role in empirically informed debates within the philosophy of psychology about people’s ordinary natural kind concepts. Those debates have sought to accommodate an apparent fact about ordinary people’s judgments: Intuitively, the Twin Earth liquid is not water. We present results from four experiments showing that people do not, in fact, have this intuition. Instead, people tend to have the intuition that there is a sense in which the liquid is not water but also a sense in which it is water. We explore the implications of this finding for debates about theories of natural kind concepts, arguing that it supports views positing two distinct criteria for membership in natural kind categories – one based on deeper causal properties, the other based on superficial, observable properties.

Keywords: Concepts, essence, essentialism, natural kinds, experimental philosophy, Twin Earth

Suggested Citation

Tobia, Kevin P. and Newman, George and Knobe, Joshua, Water Is and Is Not H2O (March 14, 2017). Mind & Language, Forthcoming. Available at SSRN: https://ssrn.com/abstract=2933100 or http://dx.doi.org/10.2139/ssrn.2933100

Kevin P. Tobia (Contact Author)

Georgetown University Law Center ( email )

600 New Jersey Avenue, NW
Washington, DC 20001
United States

HOME PAGE: http://www.law.georgetown.edu/faculty/kevin-tobia/

George Newman

Yale School of Management ( email )

135 Prospect Street
P.O. Box 208200
New Haven, CT 06520-8200
United States

Joshua Knobe

Yale University

New Haven, CT 06520
United States

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