Twin Earth the philosopher Hilary Putnam took an idea raised by Edmund Husserl and in his work The meaning of meaning poses the following dilemma: There are two identical Earth planets, except that one has H2O water and the other XYZ water. It runs, then, from whether two equal persons, one on each planet, understand different things regarding the concept of water. Today, in the incessant search for a habitable planet that orbits a star that emits light like our sun, we also talk about a twin planet or EARTH TWO.
