The subject of classical harmony necessitates a deep examination of the interconnections between different keys. This relationship, first of all, is carried out by the similarity of several keys with common sounds (including key characters) and is called the relatedness of keys. First you need to clearly understand that, in principle, a universal system that determines the degree of relatedness of tonalities does not exist, since each composer perceives and implements this relationship in his own way. However, nevertheless, in musical theory and practice some systems exist and are firmly established, for example, Rimsky-Korsakov, Methodin, Hindemith and few other musicians.
The degrees of relatedness of keys are determined by the proximity of these keys to each other. The criteria for proximity are the presence of common sounds and consonances (mainly triads). Continue reading