Density of chosen harmonic devices (quantity of degrees within) affects few crucial parameters of music: construction of arpeggio based melodic phrases, mix of prevailing intervals and force of functional gravity.
Triads have thinnest texture; prevailing intervals are thirds, fourths and their inversions. Functional gravity is evident (heavily determined by Western cultural environment).
In seventh chords we observe denser texture and greater variety of intervals: seconds and sevenths become common, tritones are much more frequent. Functional gravity is the same, excepting dominant seventh chords – those pull even stronger.
Pentatonics also could be considered as vertical formations, with very dense texture. In such conditions fourths, seconds and their inversions start prevail. Functional gravity becomes weak. Looks like the vertical and horizontal of music got really close to each other. Some modes have no more than five harmonically stable tones (phrygian, for instance), all remaining act like passing or chromatic.
Next list shows how superimpositions could be categorized by density of texture: into triads, seventh chords and pentatonics. Pentatonics are marked in bold font; some of them are not common minor/major type and would be explained in further posts.
Pentatonic is powerful but yet underestimated harmonic device. I think it is because of limited intervalic structure of minor/major pentatonic (which lack some of characteristic intervals: m2, M7, tritone). Musicians are trying to alter pentatonics to fit whole range of musical structures, but they often fail to discover fundamental unifying principle. Hope I found simple and sufficient method how to overcome intervalic limitations of pentatonics and control them vertically. Great deal of upcoming materials would be entirely dedicated to this subject.