In addition to the 7th (major) scale degree, the flat second (and sometimes flat sixth) also operates as a leading tone in some music. Like scale degree 7, the flat 2 "leads" to the tonic (the flat 6 "leads" to the dominant).
This is reflected in the analytical chord notation given in Example 3.4.
Notice that the symbol for the first semitone is a downward-pointing arrow (i.e., pointing "down" to the tonic), and the symbol for the eleventh semitone is an upward-pointing arrow (i.e., pointing "up" to the tonic), in both cases reflecting the primary functional purpose of those tones.
When both lower (e.g., 7) and upper (i.e., ♭2) leading tones are used together, they are knows as a double leading tone.
The "Neapolitan" chord contains an example of an upper leading tone. In the key of C, the Neapolitan is a D♭ major chord (in first inversion), in which the A&flat (6 from minor); "leads" to G (the dominant).
[V:V1][_A_d] [GB] |
[V:V2 clef=bass][F,F] [DG,] |
The augmented sixth chord (in the context of a tritone substitution, where it leads directly to the tonic) contains a double leading tone. For example, rather than G7 leading to C, we have D♭7 leading to C. I've intentionally misspelled the D♭7 chord with B rather than C♭ to highlight the double leading tone.
[V:V1][_DF_A=B] [CEGc] |
Wikipedia has a brief discussion of the "upper leading tone". And see also Wikipedia's entry on the Lydian Cadence and its use in early music.