Tonal Preliminaries

The usual diatonic system is “dyadic,” for it privileges two intervals, the perfect octave and fifth; the usual harmonic system is “triadic,” for it privileges, in addition, the major and minor thirds (Sect. 9.1). The dyadic and triadic privileged intervals support, respectively, a dyadic/triadic notion of “consonance.” Every consonance other than the perfect prime has a unique “root,” such that, if the root is also the lower note, the consonance is “stable.” Section 9.2 studies the non-diatonic subset of the “cluster” (the set of all notes that may be received relative to the diatonic core, reduced to their register-zero representatives). It is shown that the subset consists of two length-five segments of the line of fifths, extending the seven-element core at either end to form a line-of-fifths segment totaling 17 elements exactly.