Arnold Arnstein* used the following rule: no quarter rests in 3/8, 6/8, 9/8 etc. or in the 3/8 parts of a composite meter. (He did use dotted quarter rests in these meters.) This meant that he would have notated the passage as in the first example with brackets above the notes to show the groups of three as in the attached example. The brackets were used only when there were three or four or more eighth rests in a row. For very complex music, he used beamed rests with mini stems. He used the analogous rule in 3/4, 6/8, 9/8 etc. no half rests allowed, only dotted half rests.

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Arnstein was all about simplifying difficulties for the orchestral players and almost all of his "rules of thumb" can be traced back to this desire. As circumstances arise, I will mention some of his ideas, because his wisdom should not be lost, even if one disagrees with some of his ideas. In this case, he wished to banish the complexities of notes and rests in compound meters and found this simple solution.
*A music copyist for sixty-three years, from 1926-1989, Arnold Arnstein (1898-1989) held sway as the most respected copyist of serious music in the United States. He prepared the parts for orchestral and operatic works by Samuel Barber, Leonard Bernstein, Gian-Carlo Menotti, Virgil Thomson, William Schumann, Aaron Copland, John Corigliano, Alberto Ginestera, Krzystof Penderecki, Igor Stravinsky, David Amram, and many others. Works that opened both Lincoln Center (Barber’s Piano Concerto and Anthony and Cleopatra) and the Kennedy Center (Bernstein’s Mass) were handled by Arnstein and his team of copyists.
Arnstein was an editor and authority on music notation as well as a copyist. He taught music copying at Juilliard from 1960 to 1989, and a featured article about him appeared in Time Magazine. One section of a New York Times magazine article on Barber's Anthony and Cleopatra concerns Arnstein. The Music Research Division of the New York City Public Library at Lincoln Center houses the Arnstein Collection of numerous scores and parts that were still in his possession at his death in 1989.
I worked with Arnold Arnstein daily for six years as a music copyist and assistant and witnessed many consultations between “Arnie” and prominent composers who dropped by to discuss the copying of their latest work or just smooze. I also saw young, hopeful composers leave chastened and more knowledgeable than when they arrived.
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