Commonality
How frequently a noteset appears in real music, relative to its siblings
Commonality is a rough, at-a-glance measure of how often a noteset appears across Western harmonic and melodic music. It combines melodic frequency (how often you hear it in a tune) with harmonic frequency (how often it is sounded as a chord). It is scored from 1 to 10 relative to its siblings, so the number tells you how common something is among its peers, not in absolute terms.
Siblings are grouped by shared function: intervals are compared with intervals; triads and tetrads together as one chord family; scales (modes) with scales; pentatonics with pentatonics. The most common member of each family sits at the top of its scale — the major triad among chords, ionian among modes, the perfect 5th among intervals.
Commonality usually tracks consonance but deliberately diverges from it. The tritone is sharply dissonant yet common, because it drives every dominant 7th; the dominant 7th is less consonant than the major 7th yet far more common. That gap between how a sound is built and how often it is used is itself worth noticing.