 The procedure here is often called Ramsification, or Ramseyfication. (Both spellings have occurred in print. The first is in the title of Braddon-Mitchell and Nola (1997), the second in the title of Melia and Saatsi (2006).) The effect of the procedure is that if we had a theory T which was largely expressed in the language O, except for a few terms t1, t2, …, tn, then we end up with a theory expressed entirely in the O-language, but which, says Lewis, has much the same content. Moreover, if the converted theory is true, then the T-terms can be defined as the substitutends that make the converted sentence true. This could be used as a way of eliminating theoretical terms from an observation language, if O is the observation language. Or it could be a way of understanding theoretical terms in terms of natural language, if O is the old language we had before the theory was developed.