[baudrunner]

"'meanings' just ain't in the head."

I use this partial quote of Putnam's to illustrate that the language he uses does not subscribe to that of the status quo in intellectual circles, therefore he should be taken with a grain of salt.

from Wikepedia..(my bold)

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.

In other words, Putnam's thought experiment is superfluous. In fact, there is no philosophy there, and I view it as a test to weed the wheat from the chaff, so to speak. Don't be fooled Guille, for if Putnam is indeed genuine you run the risk of losing credibility by taking him seriously. If not, you would do well to give him a passing critique.

On the actual matter of whether we should think it significant that XYZ has a different chemical composition than H2O, I believe it to be irrelevent. It is a physical comparison. Putnam places us in a time where the chemistry of the water is not known so the analysis becomes superfluous. It is water to both Oscar and Toscar. Again, there is no philosophical relevance within the context of this experiment. The real question concerns the nature of the respective realities, that even though the two substances are the same in the minds of the two, the separation of their chemistry is external to the mental appreciation in the brains of the two subjects, which have exactly the same chemical pattern related to the engrams representing their knowledge of the water. To my mind, Putnam is trying to fool a non-existant contextual framework which he does not describe and therefore which does not exist outside his thought experiment. He is detaching himself from the topic altogether by not providing that contextual framework, therefore he is a fraud.