There didn't used to be any. Schoenberg was an early numberer of every bar. But, in some manuscripts, no number 13 (12, 12a, 14...)! New notated music became so particular that it needed to be possible easily to scrutinize it beginning at any measure, in rehearsal. Old music that was part of the canon got measure numbers as it was republished, after 1900. (Nineteenth-century collected works editions didn't yet include this modernism of bar … [Read more...]