It continues to amaze me how German functional analysis is still used and taught in an idiosyncratic way, seemingly in disregard of critical approaches and enhancements of the past decades, and sometimes leading to apparent inconsistensies. Have a look at the following passage, taken from a harmony script which is currently used at a German music university. The self-referentiality and dogmatism of functional theory becomes already apparent in the title of the chapter (»The subdominant fifth-sixth chord in root position«). Your thoughts are appreciated.
»Just like the dominant, the subdominant harmony employs a characteristic dissonance: the sixth above the bass, which is also used in the S6 [= ii6] chord where it functions as a consonance. […] The added sixth [marked ›sixte ajoutée‹ in misattribution of Rameau’s concept of the same name] causes the fifth, despite being consonant to the bass, to become a dissonant note which must be correctly resolved.« (Manfred Dings, Harmonielehre I. Skript zur Übung im Wintersemester 2017/18, Hochschule für Musik Saar 2017, p. 40; see also: Wilhelm Maler, Beitrag zur Harmonielehre, Leipzig 1931, p. 15).