text: The title of a book by a Cambridge historian uses it to explain the interaction between evidence and realism.
full_question: The title of a book by a Cambridge historian uses it to explain the interaction between evidence and realism. Its existence is presented as a paradox in "The Internal Basis of Meaning" by a Wayne State philosopher. Saul Kripke used a statement defining this substance as an example of a theoretical identity statement. In a thought experiment that supports semantic externalism, Hilary Putnam imagined a “twin earth” that was identical to earth in every way except that this substance is replaced with “XYZ.” Heraclitus said that one cannot step into the same area containing this substance twice. For 10 points, name this substance that, along with air, earth, and fire, was one of the classical elements.
first_sentence: The title of a book by a Cambridge historian uses it to explain the interaction between evidence and realism.