TheHypoionian mode, literally meaning "below Ionian", is the name assigned byHenricus Glareanus in hisDodecachordon (1547) to theplagal mode on C, which uses thediatonicoctave species from G to the G an octave higher, divided at its final, C. This is roughly the same as playing all the white notes of a piano from G to G: G A B C | (C) D E F G.^[1]

Glarean regarded compositions with F as the final and a one-flat signature as transpositions of the Ionian or Hypoionian mode (depending on theambitus). Most of his contemporaries, however, appear to have continued considering such compositions as being in the fifth and sixth modes (Lydian andHypolydian), which had been regarded since the beginnings of medieval modal theory as preferring B♭ over B♮ for the fourth degree above the final, F.^[2]

• Powers, Harold S. 2001. "Hypoionian".The New Grove Dictionary of Music and Musicians, second edition, 29 vols., edited byStanley Sadie andJohn Tyrrell, 12:37–38. London: Macmillan Publishers.ISBN 978-1-56159-239-5.

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