The 12-tone method was a way of composition developed in Europe, namely Austria, in the 1920’s. There are varying opinions on how this method came about, but it is generally believed that some combination of the natural progression of traditionally tonal music and the academic fervour of trying to create something new, led to what is now termed atonality. Many composers didn’t like this newly coined term because of its negative implications. It was presumed by many critics that atonality was actually ‘anti-tonality.’ Further confusion came about when theorists said this term couldn’t be applied to mediaeval music and music of the renaissance, both of which often didn’t have this supposed tonal centre.
Eventually, a systematisation of this atonality came to light, hence serialism. Without getting too in depth as to what makes serialism different from other methods of composition I pose a few of the main facets; pitches are put into an order that is dictated by a tone row. By making this tone row we eliminate a few key elements of traditional tonality such as preferential treatment of certain pitches, tendency tones, and the magnetic push and pull of harmonic progression that comes with chords and having a dominant/tonic relationship.
To avoid ambiguity I will only use the word atonal to refer to music without an obvious tonal centre. However, occassionally I will refer to passages as being ‘more atonal’ or ‘less atonal.’