(*) Radical translation is a term by W. V. O. Quine to describe the situation in which a linguist is attempting to translate a completely unknown language, which is unrelated to his own, and is therefore forced to rely solely on the observed behavior of its speakers in relation to their environment. [wikipedia]
Then what might the self be? I propose that it is the same kind of thing as a center of gravity, an abstraction that is, in spite of its abstractness, tightly coupled to the physical world. [...] It may be a “theorist's fiction,” but it is a very valuable fiction from which a lot of true predictions can be generated. [...] What then is a center of narrative gravity? It is also a theorist’s fiction, posited in order to unify and make sense of an otherwise bafflingly complex collection of actions, utterances, fidgets, complaints, promises, and so forth, that make up a person. It is the organizer of the personal level of explanation. Your hand didn't sign the contract; you did. [...] In the same way that we can simplify all the gravitational attractions between all the parts of the world and an obelisk standing on the ground by boiling it down to two points, the center of the earth and the center of gravity of the obelisk, we can simplify all the interactions—the handshakes, the spoken words, the ink scrawls, and much more—between two selves, the seller and the buyer, who have just completed a transaction. Each self is a person, with a biography, a “backstory,” and many ongoing projects. Unlike centers of gravity, selves don't just have trajectories through space and time; they gather as they go, accumulating memories and devising plans and expectations.