Complete Encyclopaedia of Music/A/Accidental harmonies
Accidental harmonies. Koch terms the three harmonies of the key essential, and the three relatives accidental. Koch, in his Lexicon, has placed his accidental harmonies in this point of view. He considers them as connecting chords, and seems to agree with Kirnberger, who asserts that, by a species of transition, the harmony of the triad is thus united to another of its inversions.