John Canarina, Monteux’s biographer and a regular pupil in the 1950s, pointed out that there was “nothing philosophical or metaphysical” about these strictures, that they offered merely “practical advice.” Only a few of the rules, indeed, were explicitly aesthetic. “Don’t permit the orchestra to play always a boresome mezzo-forte” was one. “Don’t adhere pedantically to metronomic time” was another. Perhaps the most crucial was also the most opaque: “Don’t fail to make music.”