Twin Earth thought experiment

The Twin Earth is a thought experiment that goes back to the philosopher Hilary Putnam. It established the concept of semantic externalism. This means that the meaning of a word can not be known a priori, but that further external factors must be known. The notion of semantic externalism is not yet introduced in the original form of this thought experiment.

Situation

Given a Twin Earth, which is similar to the planet Earth in every detail. Everything is there as on earth: there is the same continents and countries, the same languages ​​and a resident who speaks German language on earth, is also responsive to the Twin Earth German. ( Earthling earthlings, engl. ) For every inhabitant of our earth exists an inhabitant of Twin Earth ( Zwillingserdling, Eng. Twin earthling ), these two differ in nothing. As the Earth is also the twin earth covered in large part with water and basic building block of life there. The Zwillingserdlinge describe exactly how the Earthlings their water than water, ie with the word " water " in their respective languages ​​.

The only difference to our earth is the chemical structure of water: while the molecular formula is true on earth, meets on the Twin Earth to the formula. Just as is also colorless, odorless, wet and quenches the thirst. Although the chemical structure is different, but the behavior is the same and the two waters are not otherwise distinguishable from each other.

To carry out the thought experiment presents Putnam two different view points before:

Follow

Both earthlings as well Zwillingserdlinge use the word "water" in the same way. On both planets, it denotes a substance with the same external characteristics. Only has this substance on the planet, the structure of a, on the other hand. It follows that, although both people with their water my wet, colorless and odorless substance that quenches the thirst, the term on earth another substance called on twin earth.

Simplified one can also imagine two completely identical people, one of whom ( person A ) lives on earth and the other ( person B) on twin earth. If A and B each have a glass of water, they have to do the exact same time and under the same circumstances, think this A to B but to.

This is the only way to determine what a person with the term " water " refers to involve their environment.

Argument

Putnam makes the following assumptions:

• ( 1) To know the meaning of an expression, is to be in a certain mental state.
• ( 2) The meaning of an expression determines the extension.

From these two premises follows:

• ( 3) A certain mental state determines the extension of the expression.

Putnam now shows among other things with the thought experiment of Twin Earth, that the conclusion (3 ) can not be true, because in a completely identical psychological state, a term can refer to two different substances and thus has different extensions. Thus, the mental state is not sufficient to establish the meaning of a term and the conclusion ( 3) is false. It follows again that the assumption ( 1) or ( 2) must also be wrong. Putnam proposes to reject assumption ( 1).

Counterarguments

• Water can be understood as a cluster concept. This means that the term " water " is not referred to, but something made ​​the seas and lakes in the form of the liquid, wet, thirst -relieving material from and I can drink. This meaning would have in common inhabitants of both earth. This counter-argument can be increased further in that it is quite people on Earth who know the meaning of " water ", but in terms of its chemical structure, are ignorant. One could argue that the chemical structure of water is actually irrelevant to the meaning of the term "water".
• Thought experiments, which differ from reality too, could be misleading because they can be intuitively understood only in the context of the actual reality.
• The assumption to construct a twin Earth, in exactly one element, here the structure of water, differs is doubtful, since each element with each other is, in many respects. So there is the mnemonic that the structure of Mickey Mouse to remember, even this would not apply to the Twin Earth.