Task: Question Generation
Input (English): Passage: Despite undergoing various changes of emphasis, Bush's music retained a voice distinct from that of any of his contemporaries. One critic describes the typical Bush sound as "Mild dominant discords, of consonant effect, used with great originality in uncommon progressions alive with swift, purposeful harmonic movement ... except in [Benjamin] Britten they are nowhere used with more telling expression, colour and sense of movement than in Bush".John Ireland, Bush's early mentor, instilled "the sophisticated and restrained craftsmanship which marked Bush's music from the beginning",   introducing him to folksong and Palestrina, both important building blocks in the development of Bush's mature style. Daula comments that "Bush's music does not [merely] imitate the sound-world of his Renaissance predecessors", but   creates his unique fingerprint by "[juxtaposing] 16th century modal counterpoint with late- and post-romantic harmony".Bush's music, at least from the mid-1930s, often carried political overtones. His obituarist Rupert Christiansen writes that, as a principled Marxist, Bush  "put the requirements of the revolutionary proletariat at the head of the composer's responsibilities", a choice which others, such as Tippett, chose not to make.   However, Vaughan Williams thought that, despite Bush's oft-declared theories of the purposes of art and music, "when the inspiration comes over him he forgets all about this and remembers only the one eternal rule for all artists, 'To thine own self be true'.".
Output (English): What is the last name of the person who wrote that the composer who retained a voice distinct from that of any of his contemporaries "remembers only the one eternal rule for all artists, 'To thine own self be true'."?