For much of the history of Western classical music, harmony has been based on scales. For instance, in the C major scale, the two most important pitches are usually C, known as the tonic, and G, an interval of a fifth up from C, which is called the dominant. Almost all pieces written before the 20th century end on the tonic and its associated chords, as this approach sounds naturally pleasing to the human ear.
Developed in the early 20th century, dodecaphony, also known as the twelve-tone technique, is a technique of composition that gives equal standing to all twelve tones (half-steps) within an octave rather than emphasizing specific pitches. Dodecaphonic compositions usually utilize groups of tones called tone rows, which can be transformed in several ways to create different melodies.
Dodecaphony was developed by the Austrian composer Arnold Schoenberg, the principal member of a group of composers known as the Second Viennese School. Many of Schoenberg’s pupils, particularly Alban Berg and Anton Webern, were exponents of the twelve-tone technique.