This post is under the working hypotheses that a melodic phrase Ph (with a complete emotional meaning) has 2 parts and melodic themes symbolized by Mt1 Mt2 and usually of opposite polarity (increasing -decreasing or vice versa) such that Mt1 is over a chord transition C1->C2 and Mt2 over another chord transition C3->C4. The quadruplet C1 C2 C3 C4 is the harmony of the melodic phrase. This quadruplet corresponds also to a pair of lines in 15-syllables poetry (8 syllables for Mt1 and 7 syllables for Mt2).
There are plenty many such quatruples inside a diatonic scale or diatonic chromatic tonality. E.g C1->C2 and C3->C4 may be both harmonic transitions , related by a melodic modulation.
In such a the quadruple there are 4 direct transitions and 2 more indirect!
We may prioritize them by the least number of chromatic transitions either direct or indirect.
We classify such 4-cycles and discuss them below.
