Twin Earth thought experiment
Encyclopedia
The Twin Earth thought experiment was presented by philosopher
Hilary Putnam
in his 1973 paper "Meaning and Reference" and subsequent 1975 paper "The Meaning of 'Meaning'", as an early argument for what has subsequently come to be known as semantic externalism
. Since that time, philosophers have proposed a number of variations on this particular thought experiment
, which can be collectively referred to as Twin Earth thought experiments.
This is the essential thesis of semantic externalism
. Putnam famously summarized this conclusion with the statement that "'meanings' just ain't in the head." (Putnam 1975/1985, p. 227)
In his original article, Putnam had claimed that the reference of the twins' 'water' varied even though their psychological states were the same. Tyler Burge
subsequently argued in "Other Bodies" (1982) that the twins' mental states are different: Oscar has the concept H2O, while Twin Oscar has the concept XYZ. Putnam has since expressed agreement with Burge's interpretation of the thought experiment. (See Putnam's introduction in Pessin and Goldberg 1996, xxi.)
referring to H2O.
John Searle
, for example, argues (Intentionality: An Essay in the Philosophy of Mind) that, once we discover that our water is H2O, we have the choice of either redefining it as H2O (a classical reduction
redefinition) or continuing to allow the term water to refer to anything with the basic properties of water (transparency, wetness, etc.). Searle suggests that in the Twin Earth example, the second seems more plausible, since if Twin Earth doesn't have water, then all its water-based products will also be different. Twin ice cream, for example, will be constitutionally different, yet we will still be tempted to call it ice cream.
Searle, along with others, considers this sufficient argument to "solve" the thought experiment altogether; others, such as Donald Davidson
feel that variations on the experiment can be used to draw some of the same conclusions.
Paul Boghossian
raised an objection to the class of Twin-Earth style arguments for externalism in the form an argument that aims to show that externalism is incompatible with privileged self-knowledge. Here, privileged self-knowledge is taken to be the idea that one can know the content of one's thoughts without having to investigate the external world (for empirical evidence). Although this type of argument does not directly disprove externalism, it is pressing because of the intuitive plausibility of privileged self-knowledge's existence.
Some philosophers believe that all such science-fiction thought experiments should be viewed with suspicion. They argue that when a thought experiment describes a state of affairs that is radically different from the actual one (or what we think it to be), our intuitions become unreliable, and significant philosophical conclusions cannot be drawn from them. Daniel Dennett
, for example, calls Twin Earth and other experiments like it "intuition pump
s", which play on a strong but ultimately illusory intuition. Indeed, Phil Hutchinson notes that a. if one looks at Putnam's own later criticisms of others (for example his criticisms of Jaegwon Kim in his book The Threefold Cord) one finds that implicitly he critiques his own earlier self; and b. that the persuasive power of the Twin Earth thought experiment/intuition pump relies on our turning a blind eye to aspects of the experiment in order that it establish that which Putnam claims it to. In short, the thought experiment is set up in such a way that one's intuitions will be pumped in the desired direction.
John McDowell
, in his paper "Putnam on Mind and Meaning" criticised Putnam for still having in play a latent commitment to a picture of the mind as modelled on the brain and located in the head. Putnam has since conceded the point and subscribes to McDowell's neo-Wittgensteinian therapeutic invocation of the mind as a structured system of object involving abilities. (What Putnam has since defended as a neo-Aristotelian picture of mind - see his papers "Changing Aristotle's Mind" and "Aristotle after Wittgenstein")
Phil Hutchinson has since argued that this concession to McDowell means that the distinction which Putnam wishes to operationalize, between intension and extension is now problematized.
John Dupre
, in a number of papers, but mainly in his paper "Natural Kinds and Biological Taxa" has demonstrated that the theory of natural kinds, which many have taken to be established and/or supported by Putnam's Twin-Earth Thought experiment does not find support in the practice of scientific classification.
Avrum Stroll
has produced probably the most comprehensive critique of the program of natural kind semantics (both Putnam's and Kripke's) in his book Sketches of Landscapes.
Putnam, who is well known for changing his philosophical positions on a variety of issues, criticizes the experiment later in life because it is anti-functionalist.
Philosophy
Philosophy is the study of general and fundamental problems, such as those connected with existence, knowledge, values, reason, mind, and language. Philosophy is distinguished from other ways of addressing such problems by its critical, generally systematic approach and its reliance on rational...
Hilary Putnam
Hilary Putnam
Hilary Whitehall Putnam is an American philosopher, mathematician and computer scientist, who has been a central figure in analytic philosophy since the 1960s, especially in philosophy of mind, philosophy of language, philosophy of mathematics, and philosophy of science...
in his 1973 paper "Meaning and Reference" and subsequent 1975 paper "The Meaning of 'Meaning'", as an early argument for what has subsequently come to be known as semantic externalism
Semantic externalism
In the philosophy of language, semantic externalism is the view that the meaning of a term is determined, in whole or in part, by factors external to the speaker. According to an externalist position, one can claim without contradiction that two speakers could be in exactly the same brain state at...
. Since that time, philosophers have proposed a number of variations on this particular thought experiment
Thought experiment
A thought experiment or Gedankenexperiment considers some hypothesis, theory, or principle for the purpose of thinking through its consequences...
, which can be collectively referred to as Twin Earth thought experiments.
The thought experiment
Putnam's original formulation of the experiment was this:This is the essential thesis of semantic externalism
Semantic externalism
In the philosophy of language, semantic externalism is the view that the meaning of a term is determined, in whole or in part, by factors external to the speaker. According to an externalist position, one can claim without contradiction that two speakers could be in exactly the same brain state at...
. Putnam famously summarized this conclusion with the statement that "'meanings' just ain't in the head." (Putnam 1975/1985, p. 227)
In his original article, Putnam had claimed that the reference of the twins' 'water' varied even though their psychological states were the same. Tyler Burge
Tyler Burge
Tyler Burge is a Professor of Philosophy at UCLA. He has made contributions to several areas of philosophy, including the philosophy of mind, epistemology, and the history of philosophy. In the history of philosophy, he has published articles on the philosophy of Gottlob Frege...
subsequently argued in "Other Bodies" (1982) that the twins' mental states are different: Oscar has the concept H2O, while Twin Oscar has the concept XYZ. Putnam has since expressed agreement with Burge's interpretation of the thought experiment. (See Putnam's introduction in Pessin and Goldberg 1996, xxi.)
Objections
A number of philosophers have argued that 'water' for both Oscar and Twin Oscar refers to anything that is sufficiently water-like (i.e. the term's extension includes both H2O and XYZ). They reject, therefore, the contention that 'water' is a rigid designatorRigid designator
In modal logic and the philosophy of language, a term is said to be a rigid designator when it designates the same thing in all possible worlds in which that thing exists and does not designate anything else in those possible worlds in which that thing does not exist...
referring to H2O.
John Searle
John Searle
John Rogers Searle is an American philosopher and currently the Slusser Professor of Philosophy at the University of California, Berkeley.-Biography:...
, for example, argues (Intentionality: An Essay in the Philosophy of Mind) that, once we discover that our water is H2O, we have the choice of either redefining it as H2O (a classical reduction
Reduction (philosophy)
In philosophy, reduction is the process by which one object, property, concept, theory, etc., is shown to be explicable in terms of another, lower level, entity...
redefinition) or continuing to allow the term water to refer to anything with the basic properties of water (transparency, wetness, etc.). Searle suggests that in the Twin Earth example, the second seems more plausible, since if Twin Earth doesn't have water, then all its water-based products will also be different. Twin ice cream, for example, will be constitutionally different, yet we will still be tempted to call it ice cream.
Searle, along with others, considers this sufficient argument to "solve" the thought experiment altogether; others, such as Donald Davidson
Donald Davidson (philosopher)
Donald Herbert Davidson was an American philosopher born in Springfield, Massachusetts, who served as Slusser Professor of Philosophy at the University of California, Berkeley from 1981 to 2003 after having also held teaching appointments at Stanford University, Rockefeller University, Princeton...
feel that variations on the experiment can be used to draw some of the same conclusions.
Paul Boghossian
Paul Boghossian
Paul Boghossian is professor of philosophy at New York University, where he held the chair for ten years . His research interests include epistemology, the philosophy of mind, and the philosophy of language....
raised an objection to the class of Twin-Earth style arguments for externalism in the form an argument that aims to show that externalism is incompatible with privileged self-knowledge. Here, privileged self-knowledge is taken to be the idea that one can know the content of one's thoughts without having to investigate the external world (for empirical evidence). Although this type of argument does not directly disprove externalism, it is pressing because of the intuitive plausibility of privileged self-knowledge's existence.
Some philosophers believe that all such science-fiction thought experiments should be viewed with suspicion. They argue that when a thought experiment describes a state of affairs that is radically different from the actual one (or what we think it to be), our intuitions become unreliable, and significant philosophical conclusions cannot be drawn from them. Daniel Dennett
Daniel Dennett
Daniel Clement Dennett is an American philosopher, writer and cognitive scientist whose research centers on the philosophy of mind, philosophy of science and philosophy of biology, particularly as those fields relate to evolutionary biology and cognitive science. He is currently the Co-director of...
, for example, calls Twin Earth and other experiments like it "intuition pump
Intuition pump
An intuition pump is a thought experiment structured to elicit intuitive answers about a problem. The term was coined by Daniel Dennett. In Consciousness Explained, he uses the term pejoratively to describe John Searle's Chinese Room thought experiment, characterizing it as designed to elicit...
s", which play on a strong but ultimately illusory intuition. Indeed, Phil Hutchinson notes that a. if one looks at Putnam's own later criticisms of others (for example his criticisms of Jaegwon Kim in his book The Threefold Cord) one finds that implicitly he critiques his own earlier self; and b. that the persuasive power of the Twin Earth thought experiment/intuition pump relies on our turning a blind eye to aspects of the experiment in order that it establish that which Putnam claims it to. In short, the thought experiment is set up in such a way that one's intuitions will be pumped in the desired direction.
John McDowell
John McDowell
John Henry McDowell is a South African philosopher, formerly a fellow of University College, Oxford and now University Professor at the University of Pittsburgh. Although he has written extensively on metaphysics, epistemology, ancient philosophy, and meta-ethics, McDowell's most influential work...
, in his paper "Putnam on Mind and Meaning" criticised Putnam for still having in play a latent commitment to a picture of the mind as modelled on the brain and located in the head. Putnam has since conceded the point and subscribes to McDowell's neo-Wittgensteinian therapeutic invocation of the mind as a structured system of object involving abilities. (What Putnam has since defended as a neo-Aristotelian picture of mind - see his papers "Changing Aristotle's Mind" and "Aristotle after Wittgenstein")
Phil Hutchinson has since argued that this concession to McDowell means that the distinction which Putnam wishes to operationalize, between intension and extension is now problematized.
John Dupre
John Dupré
John Dupré is a professional philosopher of science. He is the director of the ESRC Centre for Genomics in Society and professor of philosophy at the University of Exeter. Dupré was educated at the University of Oxford and the University of Cambridge and taught at Oxford, Stanford University and...
, in a number of papers, but mainly in his paper "Natural Kinds and Biological Taxa" has demonstrated that the theory of natural kinds, which many have taken to be established and/or supported by Putnam's Twin-Earth Thought experiment does not find support in the practice of scientific classification.
Avrum Stroll
Avrum Stroll
Avrum Stroll is a research professor at the University of California, San Diego. He is a distinguished philosopher and a noted scholar in the fields of epistemology, philosophy of language, and twentieth-century analytic philosophy.-Books:...
has produced probably the most comprehensive critique of the program of natural kind semantics (both Putnam's and Kripke's) in his book Sketches of Landscapes.
Putnam, who is well known for changing his philosophical positions on a variety of issues, criticizes the experiment later in life because it is anti-functionalist.