Putnam, Semantics, and Fake Pot

As I listened to this story on Morning Edition on the way in to the office about the dangers associated with synthetic marijuana, I couldn't help but think of one of Hilary Putnam's classic articles. The story concerns legislative reactions to deaths from inhaling synthetic compounds designed to have marijuana-like effects. According to the packaging, they are carefully sold as potpourri and labeled as not for smoking, but, of course, the manufacturers know full well to whom they are marketing and what they have to say and do to protect themselves from lawsuits. In light of the deaths, legislators have tried to ban them. But here's the problem -- what are they?

Legislators can prohibit possession and sale of marijuana because it has an identity in terms of a plant species. But these chemicals are different. Every time one is banned, the manufacturers subtly change the molecule. Now it is a different substance. Or is it?

In his paper "The Meaning of 'Meaning,'" Putnam creates one of the lasting thought-experiments in the history of philosophy. He invites us to consider Twin Earth, a place exactly like Earth, and I mean exactly. We all have doubles there who are living the same lives, having the same thoughts and experiences, everything. The only difference is on Twin Earth, the substance in the sea, that comes out of the faucet, that they wash their cars with is not H2O, but a substance with a different chemical make-up XYZ. XYZ has the same freezing point, the same boiling point, cleans dishes the same way, quenches thirst the same way, in other words is to all human experience exactly like Earth water. Of course, the people on Twin Earth cal XYZ "water." If we were to visit Twin Earth and send back a report, we'd say something like, "On Twin Earth, what speakers of Twin English call 'water' is not water, but XYZ." They mean something different by water. This is not unusual. If someone is speaking German and offers you a "Gift," don't take it. "Gift" does not mean present in German, it means poison. The symbol refers to a different referent.

But what if instead of contemporary visitors, somehow we sent people from the 1750s before there was an atomic notion of the identity of substances. For us, what we mean by water is defined by chemical composition. But for English speakers in the 18th century, there was no such sense. They would argue that they knew full well what they meant when they used the term "water," and used it properly. If take to Twin Earth, they would report that in Twin English, "water" means water. Would they be wrong since what they meant by water and what the Twin Earth speakers meant by water were, in fact the same since their notion referred to experienced properties and not chemical composition? Putnam argues that they would be wrong. We think that definitions are beyond challenge since I can define a word to mean whatever I want -- see Humpty Dumpty.

But, Putnam contends, if you are talking about a natural kind, then the world has something to say about your definition and what it says may not be so nice. The legislators find themselves in a Putnamesque world in which they are the 18th century visitors. They think they know what they mean when they say "synthetic pot," but the manufacturers are the 21st century observers who can manipulate the underlying substance. The problem is that the consumer is in the 18th century as well, so the manufacturers are playing both sides of the semantic coin.

Perhaps what we need to do is think of the term in the way that Putnam points out we treat the word "jade." Jade is not one thing, but two -- we call something made of jadite or nephrite by the word "jade." Can we do this for the sake of legislation and if so, would such ambiguity cause more legal problems than it solves?