Musically, many of his ideas were unconventional, even innovative. Some of his multi-movement compositions show 'progressive tonality' which would have been familiar to the later Danish composer, Carl Nielsen (for example, Alkan's first chamber concerto begins in A minor and ends in E major). He was rigorous in avoiding enharmonic spelling, occasionally modulating to keys containing double-sharps or double-flats, so pianists are occasionally required to come to terms with distant keys such as E# major and the occasional triple-sharp.