One of the most noted traits of Prélude à l’après-midi d’un faune is the simultaneity of its stasis and dynamics. The aberrant writing of the well-discussed opening flute theme, which stubbornly recurs eight times throughout the piece, with characteristic changes each time, is aesthetically so subversive in this regard that Boulez once claimed that “the flute of the faun brought new breath to the art of music”. However, most analysts today read the work as tonally and formally complying with traditional prototypes, despite some apparent abnormalities. In this paper, by identifying a transformational pattern of transposition-by-a-semitone-down (T-1) between two restatements of the flute theme, I rethink the tonal and formal structures of the Prélude as embodying the simultaneity in question. I contend that Debussy’s deployment of a series of related transformations can be associated with the faun’s confusion, the enigma in Mallarmé poem of whether the sensual delight and happy time he had with the nymphs came from a reminiscence of his real experience, or just a dream. I further investigate Debussy’s development of the same transformational technique in the works of Les parfums de la nuit, the second movement of Ibéria and Jeux in order to demonstrate Debussy’s sonicization of various illusions.