Tschaikovsky, Peter (1900). "XXVII". In Translated from the German version by Emil Krall and James Liebling (ed.). Guide to the Practica Study of Harmony (English translation ed.). Leipzig: P. Jurgenson. pp. 106, 108.
Christ, William (1973). Materials and Structure of Music. Vol. 2 (2 ed.). Englewood Cliffs, NJ: Prentice Hall. pp. 141–171. ISBN0-13-560342-0. OCLC257117. Offers a detailed explanation of augmented sixth chords as well as Neapolitan sixth chords.
Benjamin, Thomas; Horvit, Michael; Nelson, Robert (2008). Techniques and Materials of Music: From the Common Practice Period Through the Twentieth Century (seventh ed.). Belmont, CA: Thomson Schirmer. p. 165. ISBN978-0-495-18977-0. OCLC145143714. Beethoven frequently moves from one form of the chord to another in such a way, sometimes passing through all three.
Burnard, Alex (1950). Harmony and Composition: For the Student and the Potential Composer. Melbourne: Allans Music (Australia). pp. 94–95. OCLC220305086.