- What is the essential difference between grouping and subdivision? Thanks.

Grouping is phrasing structure, such as occurs at all level 0 and greater. The essential phrasing structure is the rhythmic cell, which is always iambic. That is, it consists of a rise associated with a following fall, and not the other way around. The BREATHS in music come between these cells, or phrases. The breaths occur after a fall, and just prior to a rise or the pick-ups to that rise.

Subdivision is what happens at levels smaller than level 0. The essential process at these levels is that of metrically dividing the level 0 beats and off beats into smaller values. These smaller level beats are, in purely metrical subdivision, rebounds of the level 0 beats and off beats. However, often there will be small breaths within the level 0 bar at irregular positions, (sometimes after a beat, sometimes after an off beat) leading to a mixture of trochaic (fall\rise) and iambic (rise/fall) associations. Also, the subdivisions themselves occur at varying levels or values (halves, quarters, eighths, 16ths, etc.). It is the organization of these small level irregularities and peculiarities of duration and association that gives each piece of music its unique rhythmical structure. At the larger levels, all music begins to appear very similar.