The next part of Putnam’s Twin Earth argument claims that if our standard of psychological difference is what is in the head, there can be no psychological differences between the speakers of both worlds. If this is true, we must then redefine the traditional concepts of meaning that have been defined by other philosophers. As of now, there are two unchallenged assumptions of the theory of meaning. The first being, “ knowing the meaning of a term is just a matter of being in a psychological state”and the second being, “the meaning of a term determines its extension”.
Putman then takes his ‘Twin Earth’ example a step further to show that in both worlds, people are in the same psychological state. He brings in Oscar from Earth and Oscar from Twin Earth, both of which have the same intention of getting water. He then takes us back to a time where no one knows what the molecular structure of water is. But even though no one knows that water is H2O, when Oscar from earth thinks of water it is H2O regardless if he knows it or not. The same goes for Oscar from twin earth. When he thinks of water, it is still XYZ regardless if he knows it or not. Therefore, both Oscars can have the same intention, but different extensions. Thus disproving that the