Skip to main content

A contra to Putnam's 'Twin Earth'

Recall than Putnam (The Meaning of 'Meaning') argued that if a new substance is discovered with a different chemical composition but the same phenomenal qualities as certain known substance, it will not fall under the same natural kind.

His thought experiment to support this claim is this: imagine a distant planet just like ours, except the water-like substance there has different, complicated chemical composition XYZ. It looks and tastes like water etc. Imagine you travel to that planet. On Putnam's reading, even though we would initially think this is water, once we discover the difference in chemical composition, we'll reject this view and reserve the term "water" for those substances which have the structure of H2O.

Here's a historical example that these things aren't so clear-cut. For ages, the Chinese considered jade to be the most precious substance (pretty much like gold in the West). They also were very sensitive to its authenticity. Near the end of the 18th century, a large shipment of a very similar stone with unrelated composition, jadeite, made it to China. The Chinese could tell by its feel that it was a different material. They called it "new jade". They also started calling the real jade '"old jade". Interestingly, both substances came to be called jade and the new jade came to be used pretty much just like the old jade (now, jadeite is even more valued than nephrite, the original jade).

[More details about this stuff in LaPorte's very nice book, Natural Kinds and Conceptual Change.]