In a newly developed system, primarily in use in the United States, notes of scales become independent of music notation. In this system the natural symbols C–D–E–F–G–A–B refer to the absolute notes, while the names "do–re–mi–fa–so–la–ti" are relativized and show only the relationship between pitches, where "do" is the name of the base pitch of the scale (the tonic), "re" is the name of the second degree, etc. The idea of this so-called "movable do," first suggested by John Curwen in the 19th century, was fully developed and involved into a whole educational system by Zoltán Kodály in the middle of the 20th century, which system is known as the Kodály method or Kodály concept.